TOKYO: Japan's Prime Minister Naoto Kan was facing media criticism on Sunday over his government's response to an explosion at a quake-hit nuclear reactor that had triggered fears of a meltdown.

"The way the government provided information is questionable," the Yomiuri Shimbun said in an editorial.

An explosion blew off the roof and walls of the structure around the reactor at Fukushima No. 1 atomic plant, about 250 kilometres northeast of Tokyo after a killer earthquake and tsunami flattened the region.

Radiation leaked from the plant, but the government moved to calm fears of a meltdown, saying that the blast did not rupture the container surrounding the reactor and that radiation levels had fallen afterwards.

The mass-circulation daily, however, noted that it took five hours for the government to deny meltdown fears after the explosion occurred, saying the slow response created unnecessary confusion among local people.

"It was too late, wasn't it?," the Yomiuri said.

The Asahi Shimbun daily, also criticising the government for indecision and delaying an expansion of evacuation areas, said in a headline: "Crisis management all mixed up. Evacuation instructions were not firm."

"It's hard, but the government should be responsible for securing people's safety by taking the worst scenario into consideration," the newspaper said.

The Mainichi Shimbun also criticised Tokyo Electric Power (Tepco), the operator of the reactor, over insufficient counter-measures against serious accidents, saying the firm had merely repeated: "This was beyond our imagination."

- AFP/cc