Japanese Prime Minister Naoto Kan visited a quake-stricken nuclear power plant in Fukushima Prefecture on Saturday and said that small amounts of radiation have been released from one of the reactors.

As he visited other areas in northeastern Japan affected by Friday's megaquake by helicopter, the prime minister saw the full extent of the catastrophe the nation now faces.

"I realized the huge extent of the tsunami damage," Kan said at a press conference upon his return to Tokyo.

The prime minister also said that Saturday is a critical day for rescue teams to find survivors.

The 50,000 rescue personnel deployed to the hardest-hit regions, including Japan's Self Defense Force, will do their utmost to help those in need, he said.

Regarding the controlled release of a small amount of radioactive steam from Fukushima No. 1 nuclear plant in order to reduce mounting pressure that could lead to a meltdown, Chief Cabinet Secretary Yukio Edano said the steam is not expected to cause any immediate threat to people's health.

"We are taking every possible measure to prevent disastrous developments," Edano said, adding that public should remain alert as more aftershocks are highly likely.

The National Police Agency said Saturday that the combined number of those who died or are unaccounted for following the 8.8 magnitude quake hitting had risen to more than 1,000.

The agency said that 398 bodies have been recovered in nine prefectures, including Tokyo.

Much of the mortal damage was caused by tsunami waves of more than 10-meters high wiping out whole cities in torrents that swept inland of Pacific coastal regions up to 12-kilometers, devouring everything in their way.

A total of 805 people are still unaccounted for following Japan 's biggest-ever earthquake disaster.

At least 15 aftershocks, from 5-6.8 magnitude, hit off Japan's east coast on Saturday following a massive 8.8 magnitude earthquake struck Japan Friday afternoon.