The container of the No.3 reactor of the troubled Fukushima No.1 nuclear power plant might have been damaged and leaked radioactive steam, the Xinhua reported.

According to the Nuclear and Industrial Safety Agency, hourly radiation near the plant was measured at 6.4 millisievert at 10:45 a.m. local time (0145 GMT), the report said.

According to the plant's officials, the fire was spotted at 05: 45 a.m. local time at the northwestern corner of the building that houses the No. 4 reactor, it added.

However, half an hour after the first sighting of flames, the blaze could no longer be seen the utility said. The cause of the fire remains unclear at this point a spokesperson for TEPCO said on Wednesday, adding that the fire apparently went out of its own accord.

The No. 4 Reactor was undergoing checks at the time of Friday's quake and was not operating, but TEPCO pointed out that they have been having problems cooling down a storage pool for spent nuclear fuel rods inside the building.