Steam was seen rising from a destroyed reactor building at the Fukushima nuclear plant in Japan, its operator announced.

Tokyo Electric Power Company (Tepco) said there were no signs of increased radiation in the area and is investigating the cause at the damaged No 3 reactor building.

The news follows a series of water leaks and power failures recently at the plant which was hit by an earthquake and tsunami in 2011. It knocked out cooling systems to the reactors, three of which melted down.

Tepco said a worker filming the site ahead of debris removal work spotted “a steam-like gas wafting through the air near the central part of the fifth floor of Unit 3”.

In its latest statement, Tepco said: “Steam-like gas is continuously wafting through the air… Although subcritical state is found to be maintained, we are ready to start standby liquid injection any time in case of emergency. We will continue to monitor the status closely.”

Cleanup at the site continues, with experts suggesting it could take around 20-30 years before the problems at the plant can be fully contained.