More than 1,000 people were believed dead and many more missing after the worst earthquake in Japan's records struck its north-east coast, unleashing a 10m-high tsunami, setting towns ablaze and sparking a nuclear emergency. The 8.9-magnitude shock triggered tsunami alerts and evacuations across the Pacific region, with Russia, the Philippines and Hawaii all moving vulnerable citizens to higher ground.
As dawn broke this morning, the full scale of the damage began to emerge. In one of the worst-hit residential areas, people buried under rubble could be heard calling out "Help" and "When are we going to be rescued?", Kyodo news agency reported. TV footage showed staff at one hospital waving banners with the words "Food" and "Help" from a rooftop.
The earthquake rocked buildings 235 miles away in Tokyo and experts said it was around 8,000 times more powerful than the recent New Zealand quake. Footage on Japan's state broadcaster NHK showed apocalyptic images of the ensuing tsunami sweeping homes, ships and trucks across the land and of buildings burning in the night.
There were unconfirmed reports of 88,000 people missing. Police said they had found 200-300 bodies in a coastal area of devastated Sendai city. Another 137 died elsewhere, with 539 injured and 351 missing. In other developments:
• Officials evacuated 3,000 people when a nuclear plant's cooling system failed, and Japan's trade minister warned of a possible of a radiation leak. Levels inside the plant have surged to 1,000 times normal. A state of emergency was issued at a second nuclear plant early this morning.
• The coastal town of Kesennuma was hit by widespread fires and one-third of the city was under water.
• Emergency response teams were searching for four missing commuter trains and a ship with 80 workers on board.
Japan's prime minister, Naoto Kan, urged people to help their neighbours and to try to minimise damage, as his the country attempted to come to terms with the destruction. "We ask the people of Japan to exercise the spirit of fraternity, help each other and act fast," he said.
Barack Obama said the earthquake was "a potentially catastrophic disaster". He warned citizens on the west coast of America to heed warnings to evacuate coastal areas. "Do as you are told," he said.
The quake happened at 2.46pm local time (5.46am GMT), about six miles below sea level and 78 miles off the east coast of Japan. The shock was felt as far away as Beijing.
Aftershocks continued for hours after the first tremor, many of more than magnitude 6.0. Joseph Tame, a Briton living in Tokyo, said concrete buildings shook as if they were made of jelly and high-rises swayed back and forth as the quake hit.
Miyagi, Fukushima and Iwate prefectures further north bore the brunt of the damage from the shock and the ensuing tsunami. Muddy torrents swept across embankments, tearing buildings from their foundations. Houses blazed as they were carried along by waves, and vehicles smashed into walls and roads, only to be dragged back out to sea as the water reversed its course. Ships crashed into harbours and footage showed a vessel struggling to escape a giant whirlpool.
In Sendai the wave carried everything in its path across miles of farmland. Thick mud, choked with cars, buses and even light planes, inundated the airport.
In Onahama, the Tokyo Electric Power Co said pressure inside the no 1 reactor at its Fukushima-Daiichi nuclear plant was rising, heightening the risk of a radiation leak, Japanese media reported early Saturday local time. The company was taking measures to release the pressure, the report added. Hillary Clinton, the US secretary of state, revealed that the American air force had flown in emergency supplies of coolant. Officials earlier evacuated 3,000 residents after the cooling system stopped working. Shaun Burnie, a consultant to the nuclear industry and former head of nuclear campaigns at Greenpeace International, said there was a very real risk of a leak if nuclear fuel inside the reactor core was left to heat up to unsafe levels. "This is a serious situation which could get very much worse. The last thing the people of Japan need after the tragedy of this earthquake and tsunami is a nuclear catastrophe."
Much of Kesennuma, a town of 70,000 people in Miyagi prefecture, was ablaze, NHK said. Japan's coastguard said it was searching for 80 dock workers on a vessel swept away from a shipyard in Miyagi. Across the north-east roads buckled, pylons toppled and buildings collapsed. Airports closed and rail services came to a standstill across much of the country. "Our initial assessment indicates that there has already been enormous damage," the chief cabinet secretary, Yukio Edano, said.
Phone voice services were out of order in much of the north-east, but data services allowed some people to contact friends and relatives. London-based Naoya Tatsuzawa said his 74-year-old father had sent an email saying he was trapped on the roof of a building north of Sendai city.
"As far as I know he was in good spirits and they were supporting each other, but it has been snowing and is very cold. It must be awful," he said. David Halton in Sendai said via Twitter: "Broken buildings. People without electricity. It's freezing."
In Tokyo millions were stranded as train services closed. Many spent the night at shelters in schools and other public buildings. Four million were without power.
Across the Pacific, scores of countries were on tsunami alert, with experts expressing particular concern about low-lying islands. Warnings were later lifted for many locations including Australia and New Zealand but experts warned that successive waves could grow larger through the day.
The US geological survey said the shock was the biggest earthquake to hit Japan since records began in the late 1800s. Japan is one of the most seismically active countries and this shock was one of several to have struck the north-east this week, including one of magnitude 7.3 on Wednesday. In 1933 a magnitude 8.1 quake in the area killed more than 3,000 people.The United Nations secretary general, Ban Ki moon, has pledged it will do "all it can to mobilise humanitarian assistance". David Cameron told a press conference in Brussels: "We stand ready to help in any way that we can."