TOKYO - A major earthquake shook the northeast of Japan late on Thursday, and a tsunami warning was issued for a part of the coast already devastated by last month's massive quake and tsunami that crippled a nuclear power plant.

Members of a Japanese rescue team listen for news on Friday in Ichinoseki, Iwate prefecture, northern Japan, after a 7.4-magnitude earthquake struck off shore at 11:32 pm local time on Thursday. The quake rattled nerves nearly a month after the devastating earthquake and tsunami that flattened the northeastern coast. [Photo/Agencies]

More than 30 people were injured, according to Japan's National Police Agency, at press time.

The 7.4-magnitude quake, which struck at 11:32 pm in Japan, halted operations at some thermal power plants in Aomori and Akita prefectures, Kyodo news agency reported.

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No damage was detected at the troubled Fukushima Daiichi plant and workers had been evacuated without reports of any injuries, operator Tokyo Electric Power Co (TEPCO) said.

"After the earthquake and the tsunami warning, all the workers evacuated to a safe area. The company confirmed all the workers have cleared the plant safely," a spokesman said.

"We have no information immediately indicating any abnormality at Fukushima Daiichi plant," a spokesman told a news conference.

Engineers, who sealed a leak this week that had allowed highly radioactive water into the sea, are pumping nitrogen into one reactor to prevent the risk of a hydrogen gas explosion, and want to start the process in another two reactors.

Nuclear power stations in Ibaraki prefecture were operating normally after the quake, while at the Onagawa nuclear plant in Miyagi prefecture, which has been suspended, two external power supply units among three have failed, according to the nuclear regulator.

Japan is struggling to bring the crippled Fukushima plant under control after the 9-magnitude quake on March 11 and the tsunami that followed, which killed an estimated 28,000 people.

Japan's neighbors have sounded increasingly alarmed over the risk of radiation from the plant, while tourists are staying away in what should be the peak season, and the country seeks ways to cut power use.

Announcers on Japan's public broadcaster NHK told coastal residents to run to higher ground and away from the shore after the quake hit on Thursday.

The Japan meteorological agency had issued a tsunami warning for a wave of up to 2 meters, but it was lifted later.

Officials say Thursday's quake hit 25 km under the sea and off the coast of Miyagi prefecture. Buildings as far away as Tokyo shook for about a minute.

In Ichinoseki, inland from Japan's eastern coast, buildings shook violently, knocking items from shelves and toppling furniture, but there was no heavy damage to the buildings themselves. Immediately after the quake, all power was cut. The city went dark, but cars drove around normally and people assembled in the streets despite the late hour.

Paul Caruso, a geophysicist at the US Geological Survey in Colorado, said Thursday's quake struck at about the same location and depth as the March 11 quake. It's the strongest of the more than 1,000 aftershocks that have been felt since, except for a 7.9-magnitude aftershock that day.

Reuters-AP-AFP