Civil Defence has issued a marine tsunami warning for New Zealand after a magnitude 8.9 earthquake struck Japan early tonight, NZ time, but says it does not expect it to pose a threat for people on land.
A wave of up to 1 metre may reach the coasts of the central and northern North Island from about 6.30am tomorrow, but the first arrival was expected to coincide with a low tide.
The Pacific Tsunami Warning Centre said in an 8.30pm (NZ time) bulletin a tsunami warning was in place for New Zealand, Australia and most countries bordering the Pacific Ocean.
"The New Zealand Tsunami Expert Panel assessment is that this is a marine threat only for New Zealand," Civil Defence said just after 10pm.
"A Marine Threat means strong and unusual currents are possible in the sea, rivers and estuaries. No land threat is expected at this time."
Past experience and tsunami models indicated that the largest impact would be a wave of up to 1m reaching East Cape northwards and from Kaipara northwards.
Waves would continue for several hours, and the first one may not be the largest, Civil Defence warned.
The last place expected to be hit would be Nelson, about 11.15am.
The Ministry of Civil Defence Emergency Management and scientific advisors were closely monitoring the situation to determine the severity of the threat to New Zealand.
People in New Zealand coastal areas were warned to stay off beaches and out of the water.
A 4-metre tsunami washed away cars and tore away buildings along Japan's eastern coast near the epicentre after the massive earthquake hit at 2.46pm (6.46pm NZT).
The death toll had reached 19, press reports said tonight, and officials were trying to assess damage, injuries and deaths from the quake but had no immediate details.
There are an estimated 100 New Zealanders in the northeastern part of Japan worst-affected by the quake and tsunami, a Ministry of Foreign Affairs and Trade spokeswoman said.
The number was an estimate because not all travellers registered with the embassy.
There were 3500 New Zealand registered as travelling or living in the whole of Japan and about 1600 of those were known to be in Tokyo.
The New Zealand embassy in Tokyo had reported no casualties among its staff, but the spokeswoman said there had not yet been any contact with Bunzo Kamei, a businessman who is consul in Sendai, one of the worst-affected cities. That city has a population of 1 million, and is about 360km north of Tokyo.
The quake struck at a depth of 24km, about 125km off the eastern coast, the agency said. The area is 380km northeast of Tokyo.
That was followed by a series of powerful aftershocks, including a 7.4-magnitude one about 30 minutes later.
The meteorological agency issued a tsunami warning for the entire Pacific coast of Japan. NHK was warning those near the coast to get to safer ground.
In downtown Tokyo, large buildings shook violently and workers poured into the street for safety, and TV footage showed fires across the city in buildings and at an oil refinery.
A New Zealander who is co-director of the Australian Tsunami Research Centre and Natural Hazards Research Lab at NSW University, Professor James Goff, said that though Japan had a rigorous earthquake building code and excellent tsunami warning system and evacuation plans the powerful and relatively shallow quake would likely provide a severe test.
An Australian seismologist based in Canberra, Kevin McCue, said the quake was the largest recorded in Japan.
There had been seven earthquakes in Japan over magnitude 8 since 1891.
In 1923 the 7.9 magnitude Kanto earthquake killed 147,000 people, and Mr McCue said it was likely that many people had been killed in the latest quake, even though it was further north of Tokyo than the Kanto earthquake.