The augmented reality game Pok��mon GO has taken the United States - plus Australia, New Zealand,Japan and the UK - by storm in its first week, NIU YUE reports from New York.

William Hum, a 25-year-old social media manager, was finishing his normal weekday lunch break in New York's Bryant Park when he got into a battle. He wasn't alone.

The Midtown Manhattan park had become a battleground for Pokmon (short for pocket monster) GO players that day, and Hum was one of 21 million active Pokmon GO users in the US. And he isn't alone.

The augmented reality (AR) game has swept millions into playing since being launched on July 7.

Pokmon GO is the "biggest mobile game in US history", said a report from SurveyMonkey Intelligence. According to analytics firm Sensor Tower, more than 7.5 million Americans spend an average of 33 minutes a day playing the game, topping popular social media apps like Twitter, WhatsApp, Instagram, and Snapchat. Some reports say it's closing in on Facebook in the amount of time people spend on the game.

How does Pokmon GO work?

It uses the GPS on a smartphone to track Pokmon in an augmented reality world. As players change their location, different types of Pokmon will appear randomly on their smartphone screen, and they can collect them. The goal is to encourage players to move around to catch Pokmon, which can become a collection or be used in virtual battles against one another.

Weight-loss program?

Some users have reported losing weight because they have walked so far in their hunt for Pokmons.

"I dropped five pounds in five days since I started playing Pokmon GO," said Christopher Reyes, 19, who was hunting for pocket monsters in Times Square.

Times Square has become one of the most popular locations in Manhattan for Pokmon GO, with some players saying there just aren't enough Pokmon where they live outside the city.

Top: Pokemon GO players around Manhattan. Above. left: A screenshot of a Drowzee in Times Square. Right: The map of Times Square area as it appears in the game Pokmon GO. Photos By Judy Zhu / For China Daily

"I came to Times Square just to catch Pokmons", said Jennifer Wu, who lives in Flushing, New York.

Nintendo has owned the Pokmon franchise of games and animation since the 1990s. The game Pokmon GO was developed by San Francisco-based Niantic. It is available as a free download on Android and iOS.

The need to change locations to catch Pokmon has led players to form online and offline communities.

Daniel Rodriguez, a 19-year-old student from New Jersey, was in Times Square playing Pokmon GO when he saw three others playing the game and joined them. "You can't be at home. You have to walk, meet new people, and make friends," said Rodriguez.

Some Chinese in New York City have also formed online communities for sharing information about where to collect Pokmon.

"A guy shared a location where he caught a Pikachu yesterday in WeChat, then I followed his route to Times Square, and now I have collected four!" said Daniel Lu, a member of a 15-player WeChat group named "Pokmon NYC".

Andrew Garrahan, a founder and game programmer at Computer Lunch in New York City, said Pokmon GO has become a phenomenon because of the advanced digital map technology it uses from Google and the universal use of smartphones.

"One of the strengths Niantic has is that it is a spinoff of Google, and they have access to the Google Map data, one of the best data sets today. So the company is in the best situation to do a good job with the Pokmon franchise," he said. "Especially in a time when everybody has a smartphone."

Even with its technology and high popularity, there are complaints about the game's design and operation.

"I think this game has strong geographical discrimination. I couldn't catch any other things except Weedle (a worm-like Pokmon) and Zubat (bat-like Pokmon) in New Jersey. I have even asked my friend in New York City to log into my account and help me play," said Effie Fang, 26, a Pokmon player in New Jersey.

Pokmon are hidden in streets, and there are also many Pokstops located at places like public art installations, historical landmarks, graffiti, subway stations and monuments, where players can collect Pok Balls and other tools for catching wild Pokmon.

Some wild Pokmon will appear only in certain places with higher population densities or a specific natural environment, such as water-type Pokmon appearing near lakes and oceans.

Lynn Wilson, 27, a Long Island resident, saw obvious differences between Pokmon types and their numbers in different areas.

"I just played for half an hour in Times Square, and I've already collected four rare Pokmon. It's more than the number I could get walking around nonstop in Long Island for half a day," she said.

Random placement

As a virtual reality game designer with six years' professional experience, Garrahan, however, said the difference is unlikely the result of an intentional design.

"They might have designed a complicated program with a higher level code to randomly place the Pokmon and Pokstop in different places. But as they are not doing it by hand, there's absolutely no geographical discrimination in the designing process," he said.

Others complain that the Pokmon GO server crashes too often when it is overloaded with players.

Paul Michael, 26, a Pokmon trainer since the game was introduced, said he felt frustrated after spending "centuries" waiting for the server to restart.

"I almost caught an Aerodactyl (a rare dragon-like Pokmon) half an hour ago, but the server went down. I hated my life a little bit when it happened," he said, still trying to reload the game.

It's not the first time the game's design has been criticized as faulty. Shortly after its release on July 7, Pokmon GO was reported to be seeking full access to a user's Google account, which raised concerns about privacy. The developers acknowledged the flaw on Tuesday, five days after the game's release, and issued updates to ensure users' information was protected.

Other safety concerns arose when the game went beyond the internet. Some people worried that players become less aware of their surroundings when they are immersed in the half-fantasy world the game creates.

"Many players are like zombies in the streets", said Sandra Chen, 30, a Pokmon player in New York City. "They keep their heads down, starring at the screen in case a Pokmon pops up."

Kyrie Tompkins, a Maine web designer, twisted her ankle trying to catch a Pokmon. "My ankle still hurts and I missed the Jigglypuff (a small pink Pokmon)," she tweeted on July 7.

Emergency room trip

Reddit user "Amalthea" said that "Pokmon GO put me in the ER" on July 7.

"Not even 30 minutes after the release last night, I slipped and fell down a ditch. Fractured the fifth metatarsal bone in my foot, six to eight weeks for recovery," said "Amalthea".

A police station in San Francisco issued Pokmon GO safety tips to remind players of potential dangers, asking players to obey traffic laws, avoid running into obstacles and stop riding bikes or skateboards while playing the game.

The Metropolitan Transportation Authority sent a tweet on Monday alerting players to not get close to train tracks when playing Pokmon GO in subway stations.

"It says in the beginning of the game, 'stay aware of your surroundings'," said Reyes. "I always tell myself the road is not where the Pokmon are going to appear. They are going to be right down the sidewalk, so I either catch them before going across the road, or wait until I get across first."

Despite the drawbacks, Pokmon GO players and the game's developers are positive about its future and also the AR game market.

"This is the most popular AR game that ever existed. We are definitely going to see a lot of clones," said Garrahan.

Judy Zhu and Nancy Kong in New York contributed to this story.

Pok��mon GO and bizarre incidents

Pokmon GO has been making headlines since its release, and not just for its popularity. Players have been led into a variety of bizarre situations, including finding a dead body.

On July 8, Shayla Wiggins was trying to catch a water Pokmon at a river in rural Wyoming and stumbled upon the body.

"I probably would have never gone down there if it weren't for this game," the 19-year-old told CNN. "But in a way, I'm thankful. I feel like I helped find his body. He could have been there for days."

Seth Ortega and Javier Soch were playing the game in Fullerton, a district of Los Angeles, when they noticed a man acting strangely, police told The Los Angeles Times.

They told police that he had approached a woman with two children, who were also playing Pokmon GO, and that he had started touching the foot and leg of one of the children. The man was arrested for child annoyance. Officers then discovered that he had an outstanding warrant for attempted murder in Sonoma, California.

Police in O'Fallon, Missouri, a suburb of St Louis, arrested four teens on Sunday after a robbery victim called police from a convenience store, according to a police statement.

"Using the GPS feature of the Pokmon GO app, the robbers were able to anticipate the location and level of seclusion of unwitting victims," police said. Using a handgun, the teens then robbed nearly a dozen Pokmon Go players using a handgun, police said.

The San Francisco police department published safety tips, including one specific alert saying "Tell your kids about stranger-danger because the app may bring strangers together in real life at 'Pok-stops'."

Developers of the "augmented reality" game urged players to take precautions as they tracked down characters like Pikachu using the GPS mapping and camera systems on their devices.

"We encourage all people playing Pokmon GO to be aware of their surroundings and to play with friends when going to new or unfamiliar places," Pokmon Company International and Niantic said in an emailed statement.

Judy Zhu and Nancy Kong in New York contributed to this story.

(China Daily USA 07/15/2016 page20)