Water containing radioactive material has leaked from a pressure vessel inside a reactor at the Tokai No. 2 nuclear power plant in Ibaraki Prefecture, the government's Nuclear and Industrial Safety Agency said Wednesday.

According to the agency, the plant, operated by Japan Atomic Power Co. and located just north of Tokyo, may have lost around 64 tons of water from its pressure vessel, which escaped into an outer container housing its boiling water reactor.

The plant's operator said that workers mistakenly loosening a screw on the lower side of the vessel led to the water leaking and dousing four workers, although Japan Atomic Power Co. said none of their workers involved tested positive for internal radiation.

According to a statement made by the operator, an alarm sounded at the plant at 10:20 a.m. local time and workers arrived at the vessel to find water leaking from a pipe. Japan Atomic Power Co. confirmed at 2:14 p.m. local time that the leak had been contained.

Operations at the Tokai facility automatically halted following the massive March 11 earthquake hitting the eastern seaboard of Japan and operations have since been suspended for regular checkups.

Japan Atomic Power Co. said that the nuclear fuel, which can usually be found inside the pressure vessel, had been moved to a spent fuel pool due to the reactor being checked, and currently confirmed water levels in the pool have been maintained.

Local prefectural officials as well as regular citizens from the densely populated Tokai village that plays host to the plant have been urging the central government to decommission the 33- year old plant.