A second hydrogen blast has been reported at Fukushima No. 1 nuclear power plant, this time at Reactor No. 3, the government's nuclear safety agency said Monday, according to a Kyodo News.

The first hydrogen explosion at the same plant took place on the No. 1 reactor on Saturday.

Japanese officials had been injecting seawater into overheating nuclear reactors on Sunday, in an attempt to relieving pressure at the plant.

The No. 3 reactor at the Fukushima No. 1 plant may have been deformed due to overheating, Chief Cabinet Secretary Yuko Edano said earlier in the day.

He denied that there had been a meltdown at the plant. Such a condition occurs when nuclear fuel rods melt in the reactor.

He also said another hydrogen explosion could take place at another reactor in the facility, similar to one on Saturday that blew off part of the building which housed another reactor at the same plant.

The reason is that large amounts of hydrogen formed when a water injection procedure ran into some temporarily problems that may have filled part of the building housing reactor No. 3, Edano said.

Plant operator Tokyo Electric Power Co. had been injecting water into the No. 3 reactor's core vessel on Sunday.

An evacuation area of 12 miles around the plant has been in place since Saturday, after being expanded from 6 miles.