The operator of Japan's troubled Fukushima Daiichi nuclear power plant says steam is rising from one of its damaged reactor buildings, but stresses there is no cause for alarm.
The Tokyo Electric Power Company says the vapor was spotted early Thursday around the fifth floor of the number three reactor building, which was damaged in a 2011 earthquake and tsunami.
TEPCO says radioactivity levels around the facility have not changed. It does not believe it is an emergency situation.
The operator is still investigating what caused the vapor. A spokesperson says one explanation is that rain may have come into contact with a heated reactor container and evaporated.
The plant has suffered serious safety setbacks in recent days, including leaks of water contaminated with radiation. TEPCO recently acknowledged there have been significant increases in levels of radioactive substances in soil and water samples at the plant.
Workers continue to pump water over the damaged reactors to keep them from overheating. But the contaminated water is building up quickly and TEPCO says it is running out of space to store it.
A massive earthquake and tsunami in March 2011 shut off the plant's power and cooling systems, causing a meltdown in three nuclear reactors. It was the world's worst nuclear disaster since the 1986 Chernobyl accident in the Soviet Union.
Since the 2011 disaster, most of Japan's nuclear reactors have been shut down for safety inspections.