According to a report by China's Xinhua news agency, JNISA has confirmed that an explosion occurred at around 11:08 a.m. local time on Monday and was likely triggered by a combination of oxygen and hydrogen mixing.
Tokyo Electric Power Co. said that 7 missing and 3 injured after explosion at the nuclear plant.
The agency said that the wall of the reactor building has collapsed, confirming eye-witness reports that only the buildings skeletal structure remains.
The likelihood of high levels of radiation affecting people in the area is low, said the agency, but warned the 600 people that still remained within the 20-kilometer evacuation zone should leave immediately.
The agency also said that large amounts of hydrogen have amassed in the upper parts of the reactor building and that the pressure in the reactor building remains unusually high, similar to the situation with the No 1 reactor building, which also exploded on Saturday.
Cooling operations at the reactor are still continuing to ultimately preserve the containment unit, although coolant levels are low, the agency reported.
JNISA had independently verified, however, that the containment vessel in the reactor is still intact.
Speaking at an emergency press conference Chief Cabinet Secretary Yukio Edano announced Monday the explosion did not damage the reactor and containment vessel and that there is little possibility of mass radiation being leaked into the air.
Edano had feared Sunday that a hydrogen explosion could occur at the plant's No 3 reactor -- the latest reactor to face a possible meltdown, following a hydrogen blast on Saturday in the plant's No 1 unit.
Crippled by Friday's massive earthquake and tsunami, workers have been battling to stave off multiple reactor meltdowns at the faltering Fukushima plant.
More than 180,000 people have evacuated the area, and up to 160 may have been exposed to radiation, latest figures show. - BERNAMA