Japanese rescue workers and canine units searched urgently through rubble on Wednesday ahead of predicted bitter cold and heavy rain in what the Prime Minister called a race against time after powerful earthquakes killed at least 73 people in western Japan.

Ishikawa prefecture and nearby areas were shaken by a 4.9 magnitude aftershock on Wednesday — one of dozens that have followed Monday’s magnitude 7.6 temblor centred near Noto, about 300km from Tokyo on the opposite coast. The quake set off tsunami warnings, followed by waves measuring more than 1 metre in some places.

The first 72 hours are especially critical for rescues, experts say, because the prospects for survival greatly diminish after that.

“More than 40 hours have passed. This is a race against time, and I feel that we are at a critical moment,” Prime Minister Fumio Kishida told reporters. “We have received reports many people are still waiting for rescue under collapsed buildings.”

The narrow Noto Peninsula has added to the challenges in reaching some communities. Water, power and cellphone service were still down in some areas.

Naomi Gonno says she and her children got out of their house just as it came crashing down.

But her children were screaming “Granma”, and Gonno saw that her mother was trapped under the smashed house, with only her hand visible. She was able to squeeze her way out through a tiny space, Gonno said. “I can’t believe we’re still alive,” she said. “We are living in fear.”

Relief officials handed out water, blankets, food and other supplies. Search dogs joined military personnel and firefighters trying to find dozens of people who are thought to be trapped, although the exact number is unclear.