The stricken Fukushima nuclear plant has been opened up to journalists for the second time, weeks ahead of the anniversary of the March 11 disasters.

Plant manager Takeshi Takahashi said the task of the more than 3000 people there was to make sure the reactors were made safe and that no radioactive substances escaped.

The tour revealed that reactor number three had been left a mess of tangled metal, while the top floor appeared to have been blown away.

Reactor one is now completely covered with a tarpaulin-like structure.