UPDATE: From Kyodo News:

More from Kyodo News

Radiation is feared to have leaked after the container vessel suffered damage at the No. 2 reactor of the quake-hit Fukushima No. 1 nuclear power plant Tuesday morning, Tokyo Electric Power Co. said.

The utility also admitted that a critical situation called ”meltdown” in which fuel rods melt and are destroyed is possible at the plant where three reactor cores are believed to have partially melted following Friday’s magnitude 9.0 earthquake that hit northeastern and eastern Japan.

An explosion was heard early Tuesday morning at the reactor and the radiation level temporarily shot up later, the firm said as it continued efforts to prevent overheating of exposed fuel rods.

Shortly after the apparent blast at 6:10 a.m., which appears to have damaged the reactor’s pressure-suppression system, the radiation level exceeded the legal limit to reach 965.5 micro sievert per hour before jumping to 8,217 micro sievert at 8:31 p.m., it said.

The maximum level is more than eight times the 1,000 micro sievert level to which people can be exposed in one year.