Hurricane Patricia, a category 5 storm, is seen approaching the coast of Mexico in a NOAA satellite image taken by GOES East at 10:45 ET (14:45 GMT) October 23, 2015. [Photo/Agencies]

Roberto Ramirez, head of Mexico's federal water agency, said Patricia was so strong it could possibly cross the country and head over the Gulf of Mexico to the United States.

Writing from 249 miles (401 km) above Earth on the International Space Station, US astronaut Scott Kelly tweeted an imposing image of the giant storm, blanketing a significant portion of the globe in white cloud, along with the message: "Stay safe below, Mexico."

"If you are in the hurricane warning area, make preparations immediately to protect life and property," the US Embassy in Mexico.

Still, the US National Hurricane Center (NHC) said the storm should weaken once it hits western Mexico's mountainous terrain.

HUNKERING DOWN

In Puerto Vallarta, the heart of a string of resorts that range from low-end mega hotels to exclusive villas attracting tech billionaires and pop stars, loudspeakers earlier blared orders to evacuate hotels. The streets emptied as police sirens wailed.

Officials said 15,000 domestic and foreign tourists were evacuated from Puerto Vallarta.

The government warned that ash and other material from the volcano of Colima, about 130 miles (210 km) from Puerto Vallarta, could combine with massive rainfall to trigger "liquid cement"-style mudflows that could envelop nearby villages.