Officials said a second hydrogen explosion has occurred at the Fukushima Daiichi nuclear power plant in Japan, the Japanese broadcaster NHK reported Monday morning.

But the inner reactor container was intact after the explosion, an official said, and little radioactivity was dispersed.

Tokyo Electric Power Co. said three people were injured and seven were missing in the explosion.

Interactive map Nuclear power plants affected by Japan quake and tsunami:

Residents within 20 kilometres of the plant had been advised to stay indoors, NHK said.

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A soldier stops for water in Koriyama, Japan, on Sunday, two days after a giant quake and tsunami struck the country's northeastern coast. ((Mark Baker/Associated Press))

The explosion at the Fukushima Daiichi Unit 3 had been feared earlier Sunday.

On Saturday, Unit 1 at the plant blew up, but little radiation leaked because the reactor container didn't break.

With the the cooling systems disrupted by the tsunami Friday, the heat had been building up.

Operators lost the ability to cool three reactors at Daiichi and three more at the nearby Fukushima Daini complex

They had been dumping seawater into Units 1 and 3, even though that will destroy the reactors.  

On Monday morning officials had issued another tsunami warning for the same reagion that was devasted Friday, but quickly called it off.

With files from The Associated Press