Japan safety agency: roof cracked at Fukushima No 4 reactor

TOKYO (Reuters) - Two workers are missing after Tuesday's explosion at one of the reactors at a crippled Japanese nuclear plant, the country's nuclear safety agency said.

The agency did not identify the missing workers, but said they were in the turbine area of the No.4 reactor at the Fukushima nuclear plant, which was damaged by last Friday's earthquake and tsunami.

Agency official also told a news conference there was a crack in the roof of the reactor building.

Authorities are desperately trying to prevent the water which is designed to cool the radioactive cores of the plant's reactors from running dry, which would lead to overheating and the release of dangerous radioactive material into the atmosphere.

It was possible the water in the reactor was boiling, the agency said.

(Reporting by Terril Jones)