New Zealand officials have raised their tsunami alert, after earlier saying there was no threat to land.
"A minor land threat - wave heights just over one metre - now exists",civil defence said in a bulletin, warning people in coastal areas to stay off beaches.
Prime Minister John Key said he watched "in horror" the scenes from the earthquake and tsunami and said New Zealanders' thoughts were with the victims in Japan, which sent rescue teams to Christchurch to help recover bodies after a quake struck there recently.
"Our hearts go out to the Japanese government and its people," he said, extending sympathy to those who have been caught up in "this most terrible event."
Japan responded to New Zealand's own tragic earthquake with enormous support, and we are ready to help our friends in Japan at this time of need in whatever way we can.
There are 756 New Zealanders known to be in Japan, with about 100 in the worst-affected northeastern area, a foreign ministry spokesman said.
The Red Cross has set up a website to help people who are looking for family members hit by the earthquake and tsunami.
People both in Japan and abroad can register names on the site or consult the list, while those in Japan can
inform their family and friends that they are safe and provide contact details. In a statement, the ICRC said:
Thousands of people in Japan and elsewhere have lost contact with family members because of the earthquake and tsunami ... the main areas affected are the prefectures of Miyagi, Fukushima, Tochigi and Ibaraki.
Online scammers may try to exploit the twin disasters in Japan, computer users are being warned. The US Computer Emergency Readiness Team said:
Phishing emails and websites requesting donations for bogus charitable organisations commonly appear after these types of natural disasters.
The death toll from the earthquake and subsequent tsunami is expected to reach at least 1,000.
Officials at the Fukushima Daiichi nuclear power plant will release "slightly radioactive vapour" to ease pressure in one of the reactors after the cooling system failed following the huge earthquake.
The reactor had earlier shut down, but power was cut to the pumps delivering coolant to the reactor. Japan's nuclear safety agency says pressure inside one of the reactors reached 1.5times the level considered normal.
The US air force has also flown in nuclear coolant material, Hillary Clinton revealed earlier.
Japan has requested "a limited number" of search and rescue teams from the UN, says a UN spokesman.
Here's the full text of what US President Obama had to say about Japan earlier this morning (2:35am Japan Standard Time):
I want to say a few words about the terrible earthquake and tsunami that struck Japan earlier today.
First and foremost, our thoughts and our prayers are with the people of Japan. This is a potentially catastrophic disaster and the images of destruction and flooding coming out of Japan are simply heartbreaking. Japan is, of course, one of our strongest and closest allies, and this morning I spoke with Prime Minister Kan. On behalf of the American people, I conveyed our deepest condolences, especially to the victims and their families, and I offered our Japanese friends whatever assistance is needed.
We currently have an aircraft carrier in Japan, and another is on its way. We also have a ship en route to the Marianas Islands to assist as needed. The Defence Department is working to account for all our military personnel in Japan. U.S. Embassy personnel in Tokyo have moved to an offsite location. And the State Department is working to account for and assist any and all American citizens who are in the country.
Tsunami warnings have been issued across the Pacific, and we’ve already seen initial waves from the tsunami come ashore on Guam and other U.S. territories, in Alaska and Hawaii, as well as on -- along the West Coast. Here in the United States, there hasn’t been any major damage so far. But we're taking this very seriously, and we are monitoring the situation very closely. FEMA is fully activated and is coordinating with state and local officials to support these regions as necessary. And let me just stress that if people are told to evacuate, do as you are told.
Today’s events remind us of just how fragile life can be. Our hearts go out to our friends in Japan and across the region and we’re going to stand with them as they recover and rebuild from this tragedy.
Though this map of overnight shelters in Tokyo may not be hugely useful if you don't read Japanese, it does show the sheer number of places that have been set up to provide safe accommodation for those who cannot return home. The map has been provided courtesy of freelance journalist Nobuyuki Hayashi - @nobi
And if you would like a live version of the map, click here.
Another earthquake has just struck north-west Japan - this one measuring 6.6 on the Richter scale. This is pretty strong, though the quake which hit 23 hours ago measured 8.9.
Despite the smaller magnitude, the risk of this event - and more potential small quakes to come - stems from the fact that many buildings not completely destroyed have already been significantly damaged, and remain vulnerable.
At a magnitude of 8.9 on the Richter scale, the earthquake off the coast of Japan is being described as one of the worst in recorded history. It struck undersea off the east coast of Japan's northern Honshu island and sent devastating tsunami waves crashing ashore, killing hundreds.
Night has now fallen over Japan as the search and rescue effort begins - but it promises to be a massive undertaking. Al Jazeera's Laurence Lee reports on the twin disasters overwhelming the nation.
This amzing footage has been posted online, purporting to show the devastating effect of the tsunami wave on the city of Miyako in Iwate, north-east Japan.