A fire broke out in the turbine building of Onagawa Nuclear Power Plant after the 8.9 magnitude earthquake that struck Japan today and triggered a huge tsunami. There is also a fire at a nuclear reactor which is burning out of control.

The Japanese government has declared a nuclear power emergency situation following Friday's devastating earthquake, although the prime minister, Naoto Kan, said that there had been no reports of radiation leaks at any of the country's nuclear facilities.

The chief cabinet secretary, Yukio Edano, said the nuclear power plant in Fukushima developed a mechanical failure in the reactor cooling system after it was shut down during the earthquake.

He said the measure was a precaution and there was no radiation leak at the Fukushima No 1 power plant. He said the facility was not in immediate danger.

"Parts of nuclear plants were automatically shut down but we haven't confirmed any effects induced by radioactive materials outside the facilities," Kan said.

The UN nuclear watchdog in Vienna saidthe four Japanese nuclear power plants closest to the earthquake have been safely shut down.

Tokyo Electric Power said the power had been cut to 4 million homes. Among other reports of damage, Japanese media reported a fire at JFE Holdings' steel plant in Chiba. JFE, the world's fifth-largest steelmaker, said there was no major impact. Cosmo Oil said its Chiba refinery had been hit by a fire in storage tank, and it was still working to extinguish it. JX Nippon Oil, Japan's top refiner, halted operations at three refineries in Sendai, Kashima and Negishi, Jiji News said. Television showed black smoke pouring out of an industrial area in Yokohama's Isogo area.