Thousands of rescuers pressed on in their search for survivors of a New Year’s Day earthquake that killed at least 81 people in Japan, hoping to save as many as possible within a three day survival window that ends on Thursday afternoon.

“There are many people left behind in the collapsed buildings, waiting to be rescued,” Japanese Prime Minister Fumio Kishida said at a press conference.

“We will use all of our efforts to rescue as many people as possible by this evening, when 72 hours will pass since the disaster,” he said.

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 further damage to infrastructure.

Three days since the disaster struck, material aid has trickled in but evacuees remain largely cut off from food, water, warmth, and communications amid freezing temperatures and bad weather, authorities have said.