Japan tsunami and nuclear blast: how bad is it?

The devastating Japanese earthquake and tsunami threatens to become even more serious following an explosion at a nuclear power plant. The death toll is rising fast with officials now making a "conservative" estimate of 1,300 victims of yesterday's 10-metre high tsunami, which was triggered by a massive earthquake off the Pacific coast.

When and how did it happen?An 8.9 magnitude earthquake struck at 14:46 local time Friday (5:46 GMT) under the Pacific Ocean about 250 miles from Tokyo at a depth of 15 miles. Powerful aftershocks continued to hit the capital for several hours afterwards. The earthquake had been preceded by large foreshocks over the previous two days, including a magnitude 7.2 shock approximately 25 miles from today's earthquake. This is the largest earthquake to hit Japan since records began. Tremors were felt 1,500 miles away in Beijing. Technical details are available at the US Geological Survey website.

Where did the wave hit?North-eastern coastal areas of Japan, including the port of Sendai in Miyagi prefecture, were hardest hit, although the tsunami inundated the entire east coast of the country to various extents. At Sendai, the tsunami wave is thought to have reached six miles inland. Damage from the earthquake was reported from Tokyo and across Japan.

• In pictures: Japan tsunamiWhat's the damage?TV footage of the tsunami showed boats, lorries and buildings being carried miles inland. All Japanese ports have now been closed.

So far, officials fear 1,300 are dead, although this is a conservative estimate. In Sendai 200-300 people are thought to have drowned in just one ward of the city. Between 300-400 bodies were found in Rikuzentakada. In Futuba more than 90 per cent of the houses in three coastal communities were washed away.

Most worrying is a report from AFP that 10,000 people are missing in the port town of Minamisanriku.

215,000 people have fled what remained of their homes A ship carrying 100 people was swept away in Miyagi prefecture and four trains are missing.

Fires have been reported, including one at an oil refinery in Ichihara, near Tokyo. Millions of people are without electricity and the Shinkansen Bullet train service has been suspended.

In Fukushima prefecture, a dam burst, causing even more damage.

The biggest worry now is of a nuclear accident. Today there was an explosion at a nuclear power plant in Fukushima.

Will there be a nuclear meltdown? Four nuclear power plants in the earthquake zone were automatically shut down yesterday and a nuclear emergency declared.

The cooling systems in some of the reactors failed, leading to an increase in temperature. The situation is serious because if the temperature of a reactor gets too high, it can melt through its container, leading to a catastrophic release of radiation.

Emergency workers released radioactive steam from some of the reactors in Fukushima to relieve pressure building up inside.

According to one official, the amount of radiation leaking out of the Fukushima plant was more than that normally allowed in an entire year.

Despite all the efforts of the experts, however, there was an explosion at the Fukushima 1 (or Daiichi) reactor today. Video of the blast showed debris flying through the air.

Walt Patterson of the research institute Chatham House told the BBC: "This is starting to look a lot like Chernobyl."

However, Naoto Sekimura, a professor at the University of Tokyo, told Associated Press before the explosion that a disaster on the scale of Chernobyl was impossible.

"No Chernobyl is possible at a light water reactor. Loss of coolant means a temperature rise, but it also will stop the reaction. Even in the worst-case scenario, that would mean some radioactive leakage and equipment damage, but not an explosion."

However, the worst disaster in American history was at the Three Mile Island nuclear plant - a light water reactor.

Japan's nuclear agency says it is unlikely the explosion, which may have simply been a release of steam, breached the reactor.

Did the tsunami hit any other countries?Tsunami warnings were issued across the Pacific Rim, including Australia, New Zealand, the Philippines, Indonesia, Taiwan, Russia's far east, Hawaii, Chile and Oregon.

However, when the first waves started hitting Hawaii, they were under a metre high. Australia said the tsunami posed no threat, while New Zealand downgraded the tsunami warning to a marine threat.

People in coastal areas of California, Oregon and Washington were evacuated. Most seriously affected in the US was the port of Brookings, Oregon where the tsunami caused millions of dollars worth of damage.

What is the british response? Britain is sending 63 search and rescue specialist and is reinforcing its embassy in Tokyo to provide assistance to UK nationals.

Where does it rank with the 2004 Asian tsunami?So far, nowhere near as bad, although there were no nuclear reactors to contend with. The Boxing Day tsunami of 2004 was caused by a 9.2-magnitude earthquake with an epicentre off the west coast of Sumatra, Indonesia. Waves up to 20 metres high hit as many as 14 countries, killing around 275,000 people. The economic, infrastructural and human development cost of the damage was estimated to be $9.9bn. ·