The death toll has risen to 78 in the central Japanese prefecture of Ishikawa as of Thursday morning, after a series of earthquakes of up to 7.6 magnitude struck the prefecture and its vicinity.

The most stricken city of Wajima in Ishikawa has confirmed a total of 44 deaths, the national news agency Kyodo reported, citing local authorities.

In a series of aftershocks, nearly 95,000 households, as of Thursday morning, suffered water outages in several parts of Ishikawa due to water pipe damages.

Rubble and severed roads added to challenges in search and rescue operations, three days after the 7.6-magnitude quake on New Year's Day rocked Ishikawa and nearby areas, setting off tsunami warnings.

The land ministry said areas of at least 100 hectares in Ishikawa were flooded by tsunami waves following Monday's earthquakes, and the true extent of the flooding will likely be larger.

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

"More than 40 hours have passed since the disaster. This is a race against time, and I feel that we are at a critical moment," Japanese Prime Minister Fumio Kishida told a press conference on Wednesday.

"We have received reports many people are still waiting for rescue under collapsed buildings." (Xinhua)