Tokyo - Japanese Prime Minister Naoto Kan said on Tuesday that radioactive levels have become high around the earthquake-stricken nuclear power plant Fukushima following a hydrogen explosion at the site.
He said there was a high risk of radiation leaking into the atmosphere.
In a nationally televised address to the public, the prime minister urged people within 30km of the facility, located about 220km north of Tokyo, to remain indoors, not to collect washing hanging outside and switch off air conditioners to avoid air exchange with airborne radioactive substances.
"A worrisome situation remains but I hope to take the lead in overcoming this crisis," Kan said. "I will take all measures so that damage will not expand."
The prime minister called for the nation to remain calm.
Kan's remarks followed an explosion at the troubled No. 2 reactor of the quake-hit Fukushima nuclear plant on Tuesday morning, during which a critical container vessel was apparently damaged, according to the plant's operator Tokyo Electric Co. (TEPCO).
The prime minister confirmed that the radiation level had risen substantially since the blast and the risk that radiation would leak has also increased.
The radiation level, following the latest blast at the Fukushima No. 1 plant, exceeded the legal limit to reach 965.5 micro sievert per hour at 7am on Tuesday.
The reading then leapt to 8 217 micro sievert at 8.31am, the government's Nuclear and Industrial Safety Agency said.
The latest levels reported radiation levels are more than eight times the 1 000 micro sievert level to which people can safely be exposed to in one year, the agency said.
Radiation was measured at 400 millisievert near the No.3 reactor and at 100 millisievert near the No. 4 reactor at Fukushima nuclear plant around midday, public broadcaster NHK reported.
Chief Cabinet Secretary Yukio Edano said that radiation levels around the No. 3 reactor at the Fukushima plant were at levels considered "dangerous to humans," but said the readings came from the immediate vicinity of the reactor and levels would dissipate the further away from the reactor people were.
A fire at the plant's No. 4 reactor also broke out, adding to the escalating trouble at the Fukushima power plant. However, Japan's nuclear safety agency said the fire had been brought under control and the effects of the blaze were being investigated.
Tuesday's explosion was the third at the faltering plant since it was damaged in Friday's massive earthquake and tsunami.
Authorities have been trying to prevent meltdowns in all three of the Fukushima No. 1 plant's nuclear reactors, by flooding the chambers with sea water to cool them down.
Japan's central government has already asked the International Atomic Energy Agency (IAEA) as well as the US to aid the nation in managing its current nuclear crisis.
International nuclear watchdogs around the world are monitoring the situation closely and the UK and the US have dispatched nuclear experts to the scene to help local authorities with the situation.
