Some 215,000 Japanese are in emergency shelters following a devastating earthquake and tsunami which hit the country yesterday.
Hundreds are feared dead with thousands still missing as a huge relief operation swings into actions.
Rescue teams from 45 nations are on stand by or in Japan, with prime minister David Cameron saying Japan had asked for British assistance.
Teams from South Korea, Australia, New Zealand and Singapore are already on the ground, while United States president Barack Obama confirmed a US aircraft carrier was already in Japan and another was on the way.
A state of emergency has now been declared across the county following what seismologists are calling the worst earthquake ever to hit the island nation.
Cooling systems are believed to have failed at five nuclear power stations, with a huge explosion reported at the Fukushima plant, with several workers feared dead.
The 8.9-magnitude tremor struck yesterday afternoon local time, with the epicentre located off the coast of Honshu island at a depth of about 24 kilometres.
This is some 8,000 times stronger than the earth which struck Christchurch in New Zealand last month.
Japanese prime minister Naoto Kan visited the disaster zone by helicopter early on Saturday, as the army mobilised hundreds of ships and aircraft to assist the relief effort.
More than 50 aftershocks - many of them more than magnitude 6.0 - have rattled the country.
Narita Airport has been closed, disrupting travel plans for thousands of passengers.
Qantas, JetStar, Virgin Atlantic, British Airways, ANA, and Japan Airlines have all cancelled flights.
Sendai Airport has also been closed, although Haneda – the main gateway to Japan - has since reopened.
Bullet trains and subway services have also been severely disrupted in the country while tracks and tunnels are being checked.