WAJIMA, Japan -- Thousands of rescuers pressed on in their search for survivors of a New Year's Day quake that killed at least 77 people in Japan, hoping to save as many as they can within a three day survival window which ends on Thursday afternoon.

"There's little time left until it's 72 hours since the quake," Masuhiro Izumiya, the mayor of hard-hit Suzu city, said on Wednesday evening at a regional disaster response meeting.

"We really need to muster all of our remaining strength to continue rescue efforts."

Survival rates drop off 72 hours after the quake, according to emergency responders.

Severed roads and the remote location of the worst-hit areas have complicated rescue efforts. Nearly 600 tremors have hit the Noto peninsula since the main quake, raising fears of landslides and further damage to infrastructure.

"Compared to other disasters the road situation into Wajima is very bad. I feel it's taking longer than usual for assistance to arrive," Shunsaku Kohriki, a medical worker, told Reuters in Wajima city.

"I think realistically speaking the evacuees will have to live in really tough conditions for a while yet," he said.

100,000 houses without water

The full extent of the damage and casualties remains unclear four days after the deadliest quake in Japan since at least 2016. Mayor Izumiya says 90 percent of houses in Suzu may have collapsed.

All the deaths have been reported near the epicentre of the magnitude 7.6 quake in Ishikawa prefecture. More than 33,000 people have evacuated from their homes and about 100,000 houses have no water supply, officials in the area said.

Around 30,000 households remained without power in Ishikawa, according to Hokuriku Electric. Mobile providers NTT Docomo, SoftBank, KDDI and Rakuten Mobile said connectivity was still patchy in some areas.

As Japanese businesses return from the New Year holidays, manufacturers are also gauging the impact of the quake on their production lines.

Display makers Japan Display and EIZO, as well as semiconductor firm Kokusai Electric said on Thursday they were repairing damaged factory facilities. Chip material maker Shin-Etsu Chemical said its plant in Niigata restarted part of its operations on Wednesday.