Tokyo, March 12 (IANS) At least 20 aftershocks, with magnitudes ranging from 5 to 6.8, rocked Japan's east coast Saturday, a day after an 8.9-magnitude earthquake devastated the country, causing mass destruction.
The damage caused by the quake that struck Friday was amplified by tsunami waves slamming Pacific coastal regions in northeastern Japan.
At least 630 people were killed in the catastrophe, Xinhua reported, citing public broadcaster NHK.
A total of 725 people have still been unaccounted for in six prefectures.
The number of victims of the catastrophe is expected to rise to well over 1,000 people, the defence ministry said Saturday.
The National Police Agency said around 1,800 houses in Fukushima prefecture were destroyed. It said more than 215,000 people were in emergency shelters in eastern and northern Japan Saturday.
Search and rescue efforts are being conducted with the help of the US military, with around 20,000 personnel, nearly 200 aircraft and 25 boats being dispatched to the hardest-hit northeastern region.
The foreign ministry said 50 nations have offered to provide support.
Prime Minister Naoto Kan Saturday inspected a quake-hit nuclear power plant in Fukushima, where damage from a radioactive leak is feared. He also toured other affected areas.
'I realised the huge extent of the tsunami damage,' Kan told reporters after returning to Tokyo.
Almost six million households were left without power in quake-hit areas Saturday and four trains operating in the coastal regions of Miyagi and Iwate prefectures have yet to be found following the colossal tsunami.