Japan dropped its highest-level tsunami alert after issuing one following a series of major earthquakes on Monday, but told residents of coastal areas not to return to their homes as deadly waves could still come.

The quakes, the largest of which had a magnitude of 7.6, started a fire and collapsed buildings on the west coast of Japan's main island, Honshu. It was unclear how many people might have been killed or hurt. The Japan Meteorological Agency reported more than a dozen strong quakes in the Japan Sea off the coast of Ishikawa and nearby prefectures starting shortly after 4 pm local time.

At least six homes were damaged by the quakes, with people trapped inside, government spokesman Yoshimasa Hayashi said. A fire broke out in Wajima city, Ishikawa Prefecture, and electricity was out for more than 30,000 households, he said. The meteorological agency initially issued a major tsunami warning for Ishikawa and lower-level tsunami warnings or advisories for the rest of the western coast of Honshu, as well as for the northernmost of the country's main islands, Hokkaido.

Hayashi stressed that it was critical for people to move away from coastal areas. "Every minute counts. Please evacuate to a safe area immediately," he said.?The warning was downgraded to a regular tsunami several hours later, meaning the sea could still generate waves of up to 3 metres (10 feet). Aftershocks could also slam the same area over the next few days, the agency said.

Japanese public broadcaster NHK TV initially warned that torrents of water could reach as high as 5 metres (16.5 feet). The network continued to air warnings hours later as aftershocks rocked the region. People returning to get their wallets and other belongings have been known to be swept away and drowned even hours after the first evacuation warning. People were evacuated to stadiums, where they will likely have to stay for a few days.

Japanese media footage showed people running through the streets, and red smoke spewing from a fire in a residential neighbourhood. Photos showed a crowd of people, including a woman with a baby on her back, standing by huge cracks that had ripped through the pavement. Some people sustained minor injuries when they tripped and fell while fleeing, or objects fell off shelves and hit them, according to NHK.

Hayashi said no reports of deaths or injuries were confirmed from the quakes, saying the situation was still unclear. Japan's military was taking part in rescue efforts, he said. Bullet trains in the area were halted, although some parts of the service were restored by evening. Parts of a highway were also closed, and water pipes had burst, according to NHK. Some cell phone services in the region were not working. The Meteorological Agency said in a nationally broadcast news conference that more major quakes could hit the area over the next week, especially in the next two or three days.

More than a dozen strong quakes had been detected in the region, with risks of setting off landslides and houses collapsing, according to the agency. Takashi Wakabayashi, a worker at a convenience store in Ishikawa Prefecture, said some items had tumbled from the shelves, but the biggest problem was the huge crowd of people who arrived to stock up on bottled water, rice balls and bread. "We have customers at three times the level of usual," he said.

Tsunami warnings were also issued for parts of North Korea and Russia.?The Japanese government has set up a special emergency centre to gather information on the quakes and tsunami and relay them speedily to residents to ensure safety, Prime Minister Fumio Kishida told reporters. US President Joe Biden said in a statement that his administration was in touch with Japanese officials and "ready to provide any necessary assistance for the Japanese people".

Japan is an extremely quake-prone nation, but a tsunami warning of the magnitude of Monday's had not been issued since a major quake and tsunami caused meltdowns at a nuclear plant in March 2011. Government spokesman Hayashi told reporters that nuclear plants in the affected area did not report any irregularities on Monday. Nuclear regulators said no rises in radiation levels were detected at the monitoring posts in the region.