.BBC News - LIVE: Japan earthquake
Huge blast at Japan nuclear power plant
1009: "This is starting to look a lot like Chernobyl" Walt Patterson, an associate fellow with Chatham House, has told the BBC after seeing pictures of the explosion at the Fukushima-Daiichi nuclear plant. "The nuclear agency says that they have detected caesium and iodine outside the unit, which certainly indicates fuel melting at the very least," he says. "Once you have melting fuel coming into contact with water, that would almost certainly be the cause of the explosion."
1011: More from Walt Patterson of Chatham House. He says the presence of the radioactive caesium in the surrounding area does not pose a huge threat to public health in the immediate aftermath of the explosion. "What would be serious is if there was an explosion or fire that lifted this stuff high in the air, meaning it could get carried over a wide area."
1016: The BBC's environment correspondent Roger Harrabin says he understands the blast at the nuclear plant may have been caused by a hydrogen explosion - also one of the possibilities laid out by Walt Patterson of Chatham House. "If nuclear fuel rods overheat and then come into contact with water, this produces a large amount of highly-flammable hydrogen gas which can then ignite," our correspondent says.