Steam has been spotted near a pool storing machinery removed from a crippled reactor at the Fukushima nuclear power plant.

A spokesman for the plant's operator TEPCO told AFP that the steam was reported to be coming from around the fifth floor of the reactor 3 building.

"(The steam) was drifting thinly in the air and it's not like a big column of steam is spurting up," the spokesman said.

"Neither the temperature of the reactor nor readings at radiation monitoring posts have gone up.

"We do not believe an emergency situation is breaking out although we are still investigating what caused this."

The roof of the building was blown off in a hydrogen explosion just a few days after the nuclear complex was swamped by a tsunami in March 2011.

Three of the plant's reactors later suffered meltdowns.

This incident is the latest in a growing catalogue of mishaps at Fukushima that have cast doubt on TEPCO's ability to fix the world's worst atomic disaster in a generation.

A series of leaks of water contaminated with radiation have shaken confidence, as did a blackout caused by a rat that left cooling pools without power for more than a day.

ABC/AFP