Chaos followed the leak at a Japanese nuclear plant caused by a huge earthquake despite an emergency drill a week earlier, a report has revealed.

© AP/Kyodo NewsWorkers continue to clear up the debris after the Fukushima nuclear disaster.
Staff at the Fukushima facility held a disaster exercise before the March 11 crisis and 'everyone was familiar with emergency exits', said the report from plant owner Tokyo Electric Power Company (Tepco).

But it did not help their response to the actual emergency, the report revealed.

When the Unit One reactor lost cooling functions, workers tried to pump in fresh water through a broken fire pump.

And a fire engine could not reach them for hours because the tsunami that followed the quake had left a huge tank blocking the driveway.

Workers trying to release pressure from a containment vessel, to avoid an explosion, had to retrieve the manual from a separate office building, as it was not in the control room.

They also had to borrow a compressor from a contractor to activate an air- operated vent.

Protective gear had to be retrieved from a crisis management centre 5km (three miles) from the plant. It took an hour to put on air tanks, coveralls and face masks before the first two workers headed for the reactor building.

Rising radiation also disrupted the work. After one team had to abort their mission, staff switched to a less effective remote control device.

The Unit One building exploded an hour afterwards and eight workers were found to have been exposed to high levels of radiation.

Tepco and the government have said they aim to bring the reactors to 'a stable and cold shutdown' by January.

But some experts have said that is too optimistic. An independent investigation is still pending.

Meanwhile, workers were yesterday preparing to open a door on the Unit Two reactor building, to allow staff to install a cooling system and equipment to prevent an explosion.

Radioactive water is also pooling at the plant as workers scramble to restart a key cleanup system.