Officials with the Tokyo Electric Power Co. said at least 50 problems had been identified at the plant in the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture after Monday's 6.8-magnitude earthquake, the Yomiuri Shimbun newspaper reported.

The plant has been closed indefinitely following reports at least 50 percent more radioactive material had leaked into the sea from damaged exhaust ducts and toppled steel drums, a BBC correspondent reported.

"But the corrected radioactivity is also below the legal limits and does not affect the environment," a company statement said.

About 100 drums containing low-level nuclear waste fell over at a warehouse that stores about 22,000 drums of solid waste, the newspaper said.

The plant is located near the epicenter of the earthquake that killed nine people, injured hundreds and flattened many buildings.