The admission of further trouble at the seven-reactor Kashiwazaki-Kariwa nuclear plant near the epicenter of Monday's quake and delays in notifying the public triggered outrage among anti-nuclear activists and criticism from top officials.

Tokyo Electric Power Co. said a total of 50 cases of malfunctioning and trouble had been found at the plant, the world's largest in terms of power capacity, since Monday's magnitude 6.8 quake, which killed at least nine people and injured another 1,000.

The company said it was still inspecting the plant's reactors, and that it could find further problems. Four of the plant's seven reactors were running at the time of the quake, and they were all shut down automatically by the plant's anti-quake safety mechanism.

TEPCO spokesman Kensuke Takeuchi called the malfunctions "minor troubles" and said they posed no danger to the outside environment or to public health.

Cases included minor fires such as one at an electrical transformer that burned for two hours after the quake, broken pipes and water leaks, including one that flushed 1,200 liters of water containing radioactive material into the sea, the company said in a statement.

In five of the reactors, major exhaust pipes were knocked out of place and TEPCO was investigating whether they had leaked radioactive materials, the statement said. Earlier Tuesday, TEPCO said about 100 drums containing low-level nuclear waste fell over during the quake, some of the lids open.

The company also said a small amount of radioactive materials cobalt-60 and chromium-51 had been emitted into the atmosphere from an exhaust stack.

The spate of problems and TEPCO's delay in announcing them fanned concern Tuesday over the safety of Japan's nuclear power plants, which have suffered a string of accidents and cover-ups amid enduring doubts about their ability to withstand powerful earthquakes.

"They raised the alert too late. I have sent stern instructions that such alerts must be raised seriously and swiftly," Prime Minister Shinzo Abe told reporters in Tokyo. "Those involved should repent their actions."

Masanori Hamada, a professor of earthquake engineering at Tokyo's Waseda University, said the quake showed the government should push to increase the quake-resistance standards at the country's 55 reactors.

"It's unthinkable that water leaks and fire could be triggered so easily," said Hamada. "TEPCO must provide a full explanation to the public."

The mishaps at Kashiwazaki buttressed longstanding arguments by environmentalists that Japan's reliance on nuclear energy — reactors provide a third of the country's electricity — is irresponsible in a nation with such a vulnerability to powerful quakes.

"This fire and leakage underscores the threat of nuclear accidents in Japan, especially in earthquake zones," said Jan Beranek, an official at Greenpeace International in Amsterdam. "In principle, it's a bad idea to build nuclear plants in earthquake-prone areas."

In addition to the nine declared dead, one person was missing and another 13,000 quake victims were crowding emergency shelters Tuesday night as rescue workers rushed to locate any survivors amid new fears of landslides.

Victims were largely concerned with securing enough food, water and shelter for the night, but some said the threat of a devastating accident at the nuclear power plant was always at the back of their minds.

"Whenever there is an earthquake, the first thing we worry about is the nuclear plant. I worry about whether there will be a fire or something. We have no information, it's really frightening," said Kiyokazu Tsunajima, who spent the first night sleeping in his car, afraid an aftershock might collapse his damaged house.

The initial quake, which hit the region at 10:13 a.m. local time was centered off the coast of Niigata, 160 miles northwest of Tokyo. Tsunami warnings were issued, but the resulting waves were too small to cause damage.