Professor Grimes explained that any damage from Fukushima should be limited because the plant shut down as soon as the earthquake hit.

The explosion at the plant occurred 24 hours after it shut down - unlike Chernobyl, which was active when the leak occurred.

Nuclear expert Malcolm Grimston explained that the actual nuclear core had not become uncovered at Fukushima, diverting a potentially disastrous meltdown.

He told Sky News: "We know this is not a nuclear explosion, this looks like the sort of thing that happens when you demolish a block of flats it's about that level

"It could be caused by a build up of pressure - it could be fractured pipes."

He warned that it was essential to keep the plant cool over the next hours and days to avoid the incident worsening.

Reports coming from the country have indicated Japanese officials are planning to write off the plant rather than repair it.

Mr Grimston said it now seemed likely workers would flood the reactor building with sea water and boric acid - a good nutrient absorber.

"My reading of that is that they are going to write this plant off, because with sea water in there, that will cause corrosion, and the boric acid will be practically impossible to remove," he said.

Japan generates around 30% of its power from about 50 nuclear plants.