Workers at Japan's crippled nuclear plant began putting up equipment on Tuesday to allow the start of repairs to its cooling systems, key to bringing reactors under control after they were badly damaged in the March 11 quake and tsunami.

Tokyo Electric Power Company (TEPCO) has said it may take six to nine months to bring the nuclear plant back under control.

The plant operator has sent in a pair of US-made crawler PackBot robots to examine inside the reactors where radiation left by explosions is too high for humans to enter.

The company said it had begun constructing special tents at the entrance of turbine buildings so workers can move in and out. It is also installing fans with filters at the No 1 reactor to reduce radiation inside to one-twentieth of current levels within days.

"We want to suck out the air in the building and use the filter to remove radiation from the dust," TEPCO spokesman Junichi Matsumoto said.

Meanwhile, the search for the missing continued. Five hundred and sixty Japanese Self-Defense Force troops began working within a 10-kilometer radius of the plant, the Defense Ministry said, the first time they have come so close since the nuclear crisis began.

People living within a 20-km radius of the plant were evacuated and banned from returning home on April 21 due to concerns about radiation levels. And NHK reported that local governments held a two-hour rehearsal on Tuesday to prepare for when residents within the no-entry zone are allowed to return home temporarily.

The 9.0-magnitude quake and massive tsunami that followed is Japan's worst disaster since World War II and killed about 14,700 people, left some 11,000 more missing and destroyed tens of thousands of homes.

The Japanese government has estimated that compensation for damages resulting from the country's nuclear crisis could reach 4 trillion yen ($49 billion), a report said on Tuesday.

Half the money will come from TEPCO with the rest coming from other electricity companies, according to Japanese newspaper Asahi Shimbun, without citing sources.

The Japanese government has officially refused to estimate the total liability for compensation, saying that it would not put any cap on TEPCO's burden.