SENDAI, Japan – An explosion at a nuclear power station tore down the walls of one building Saturday as smoke poured out and Japanese officials said they feared the reactor could melt down following the failure of its cooling system in a powerful earthquake and tsunami.

It was not clear if the damaged building housed the reactor. Tokyo Power Electric Co., the utility that runs the Fukushima Dai-ichi plant, said four workers were injured but details were not immediately available.

SENDAI, Japan – An explosion at a nuclear power station tore down the walls of one building Saturday as smoke poured out and Japanese officials said they feared the reactor could melt down following the failure of its cooling system in a powerful earthquake and tsunami.

It was not clear if the damaged building housed the reactor. Tokyo Power Electric Co., the utility that runs the Fukushima Dai-ichi plant, said four workers were injured but details were not immediately available.