The 8.9 magnitude megaquake caused a huge wave that hit the port of Sendai city, sending ships crashing into the shore and carrying cars and buildings through streets.A ship carrying around 100 people was among those swept away.
The quake also rocked the capital, Tokyo, which one of the cities shaken by at least 20 subsequent aftershocks.
Police in Iwate prefecture, near the epicentre, confirmed the deaths of 17 people there.
Mass evacuations took place after tsunami warnings were issued for the entire Pacific basin.
But despite warnings from the International Federation of Red Cross and Red Crescent Societies, the tsunamis have reached several countries without causing major damage.
Japanese news agencies said the country had requested US forces' help in the relief effort.
The earthquake - one of the strongest ever recorded - has obliterated Tokyo's Disneyland car park and caused large fires at sites including an oil refinery in nearby Iichihara.
Large aftershocks repeatedly hit the capital, following an initial tremor so strong it was felt 1,500 miles away in the Chinese capital Beijing.
The International Atomic Energy Agency said a heightened state of alert was in effect at the Fukushima Daiichi nuclear plant, with 2,000 residents in surrounding areas urged to evacuate.
A state of emergency had also been declared at Onagawa nuclear plant in Miyagi prefecture after a fire broke out in a turbine building and an emergency cooling system failed.
But reports suggested the fire there had since been extinguished.
Japanese prime minister Naoto Kan had previously said there was no nuclear plant radiation leak caused by the disaster.
Airports and ports have been closed, while the Shinkansen 'bullet' train was stopped.
Millions of homes were left without power and Tokyo's fire department reported several people were injured when a roof caved in at a graduation ceremony in the city.
A hotel has also collapsed in Sendai, with people feared buried in the rubble.
Among the countries issued with alerts from the Pacific Tsunami Warning Centre in Hawaii were Guam, Taiwan, the Philippines, Indonesia, Thailand, Hawaii, New Zealand and Australia.
South America, Marcus Island and the Northern Marianas were also put on alert.
But authorities in Indonesia, Taiwan, Russia and the Philippines said minor tsunamis had caused little or no damage upon hitting their coastlines.
In Tokyo, large buildings shook violently and workers poured into the street for safety after the tremor struck.
Millions were evacuated in the capital as buildings continued to sway for hours after the initial quake.
Google has launched a people-finder website for those in Japan worried about the whereabouts of friends and relatives.
And a United Nations spokeswoman said international rescue teams were on alert should Japan request aid.
People in Japan have been speaking of their terror as the sea of debris swept inland.
Experts say the earthquake is the world's fifth strongest since 1900.
The Japanese government's top spokesman, Yukio Edano, said the country was sending troops to the quake-hit area to join relief efforts.
TV footage showed a large building on fire and billowing smoke in the Odaiba district of Tokyo.
Police and coast guard officials said they were assessing the scale of the damage from the quake.
Several quakes had hit the same region in recent days, including a 7.3 magnitude one on Wednesday.
A megaquake is defined as one exceeding seven on the Richter scale.
The Foreign Office can be contacted for advice on +44 (0)207 0081500.
Britons can also call the embassy in Tokyo on +81352111100 or Consulate General Osaka on +81661205600.
news provided by sky news.
In hello project related news, tsunku tweeted that all members and staff are safe and will continue to keep us updated on events as they unfold.
here at www.helloprojectxtreme.blogspot.com we are deeply upset with this news and our thoughts are with the japanese people, all activitie on this site and our sister site www.japanesextreme.blogspot.com will be suspended for today as a mark of respect and will continue to post againf tomorow evening.