Japan has been hit since Monday by 155 earthquakes including a 7.6-magnitude jolt and another over 6, the Japan Meteorological Office said.
Most of the quakes had a magnitude greater than 3 and while the strength has gradually moderated, six strong jolts were still felt early Tuesday, the JMA said.
At least six people died in a major earthquake that struck central Japan on New Year's Day, triggering tsunami waves over a metre high, damaging homes and sparking a major fire that wreaked destruction overnight, authorities said Tuesday.
The scale of the damage from Monday's quake was still emerging, with news footage showing toppled buildings, sunken boats at a port, countless charred homes, and locals without power in freezing overnight temperatures.
The US Geological Survey (USGS) said the quake, which struck Ishikawa prefecture on the main island of Honshu had a magnitude of 7.5.
Japanese authorities put it at 7.6 and said it was one of more than 90 quakes that had rocked the region as of 1:00 am Tuesday (1600 GMT Monday).
Waves at least 1.2 metres (four feet) high hit the port of Wajima on Monday, and a series of smaller tsunamis were reported elsewhere, but warnings of much larger waves proved unfounded.
Aerial news footage showed sunken boats at the fishing port of Suzu, with at least one washed onto shore, and devastation from a major fire in Wajima.
Around 32,700 households in the region remained without power on Tuesday, the local energy provider said.
Tens of thousands of people had been ordered to evacuate, according to the fire and disaster management agency, cited by Kyodo. About 1,000 people were staying at a military base, the defence ministry said.
"I instructed (emergency workers) to reach the area as soon as possible by using whatever means available," Prime Minister Fumio Kishida said late Monday after a disaster response meeting.
"It is very cold now. I issued an instruction to deliver necessary supplies like water, food, blankets, heating oil, gasoline, fuel oil, by using planes or ships," Kishida told reporters.