International rescue teams are rushing to Japan following the 8.9-magnitude earthquake and tsunami on Friday.
The American aircraft carrier USS Ronald Reagan arrived off the coast of Japan on Sunday to provide logistical support for Japanese military forces.
The Americans say Japan has asked the carrier to refuel its helicopters and help transport its troops to affected areas.
A 144-member rescue team of the US Agency for International Development is due at Misawa in northern Japan later on Sunday to join inland operations.
The team includes 12 dogs trained to detect victims trapped under rubble and about 150 tonnes of rescue equipment.
Britain is sending a 59-strong search-and-rescue team and 11 tonnes of specialist rescue equipment including heavy lifting and cutting gear.
France said it was sending two civil security teams to help with rescue efforts.
And a 66-strong Japanese team which has spent more than two weeks searching the rubble from last month's 6.3-magnitude quake in Christchurch is due back home to confront the unfolding disaster.
The UN said Japan had also accepted help from Germany, Mexico, New Zealand, Singapore and South Korea.
Rescue teams from another 39 countries are on standby.
New Zealand contribution
Members of a New Zealand Urban Search and Rescue team are due to begin arriving in Tokyo on Sunday evening.
The 48 member unit is being accompanied by 11 support staff including medics, engineers and communications experts.
The Fire Service's Christchurch Area Manager, Dan Coward, says the team and 15 tonnes of equipment are being transported by a mix of defence and commercial aircraft.
He says the Fire Service's Director of Special Operations, Jim Stuart-Black, is leading the New Zealand team.
