A 10-metre tsunami has hit the port in Sendai in northern Japan after a huge 8.9 earthquake struck off the coast on Friday, with one person reported dead.
In New Zealand, Civil Defence is advising coastal communities that a tsunami is possible here.
The Pacific Tsunami Warning Centre has now officially included New Zealand in its tsunami warning.
Also included is Nauru, Solomon Islands, Kiribati, Tuvalu, Vanuatu, Tokelau, Samoa, American Samoa, Australia, Fiji, New Caledonia, Tonga, Pitcairn and Antarctica.
BBC film shows a huge wave of mud, water, a ship and building wreckage rolling across fields and buildings near Sendai.
It also shows cars and trucks being swept off a damaged bridge into water, with boats being swept away, some overturned, and water rising around buildings.
Sendai has a population of some one million people.
Elsewhere in Japan several people are known to be buried in a landslide.
Power is said to have been cut to millions of homes.
Many sections of expressways have been damaged.
There is a major fire at an oil refinery near Tokyo and the bullet trains in the north of the country have been stopped.
One report quotes the Tokyo Fire Department as saying many people were injured after a roof caved in during a school graduation ceremony at a hall in east Tokyo.
Japan's meteorological agency issued its top-level evacuation alerts for the entire Japanese coast.
The United States Geological Survey says the earthquake struck at a depth of 24 kilometres.
It says it was centred near the east coast of the island of Honshu, 373 kilometres from Tokyo.
At magnitude 8.9 it is in the top classification, a powerful earthquake.
It follows two major quakes earlier in the area.
Numerous, strong aftershocks are continuing.