Meltdown fear
The crippled Fukushima Daiichi power plant's fourth reactor. A report reveals that scientists theorised the disaster causing the evacuation of tens of millions of people

The Japanese Government considered evacuating tens of millions of people during the Fukushima reactor disaster, a leaked document has revealed.

The worst-case scenario, which would have seen evacuations spreading as far as Tokyo, raises questions over how much the government underplayed the scale of the disaster.

An internal document obtained by the Associated Press, appears to show that officials hid the scale of their concern to avoid panic.

Then-prime minister Naoto Kan and his advisers received the report two weeks after three reactors melted down at the Fukushima Daiichi plant after it was hit by a devastating earthquake and Tsunami in march 2010.

The report, carried out by the Japan Atomic Energy Commission, suggests the scale of possible outcomes from the meltdown as well as suitable responses.

Contingencies considered possible were explosions inside the reactor and the complete meltdown of the plant.

Several escalations would mean that all workers would have no choice but to evacuate, leaving the situation to deteriorate on its own.

In a worst-case scenario, which would see huge increases in radiation levels as cooling pools fail and the plant melts down, the report calls for an evacuation of all houses within a 105 mile radius, with those within 155 miles being offered a voluntary evacuation.

The area would have included Tokyo, which has a population of 35 million, and Sendai, which has one million people. The area would remain unsafe for several decades.

The document, penned by commission head Shunsuke Kondo, states that it cannot rule out further developments that may lead to an "unpredictable situation" at Fukushima.

The government has refused to make the document public, although at the time of the disaster officials stressed the need for calm and downplayed the possibility of major evacuations.

Goshi Hosono, cabinet minister in charge of the crisis, dismissed the report as a "scenario based on a hypothesis".

"We were concerned about the possibility of causing excessive and unnecessary worry if we went ahead and made it public. That's why we decided not to disclose it," he said.

The Japanese government has repeatedly come under fire for its efforts to dampen down the scale of the crisis. At one time officials denied the reactors had melted down.

Efforts to renew confidence in the decontamination process have also met with some scepticism. In November Japanese MP Yashiro Sonoda drank a glass of water from a radioactive puddle to show that the water was safe.