KASHIWAZAKI, Japan, July 18 — The Japanese operator of a nuclear power plant stricken by an earthquake earlier this week said Wednesday that damage was worse than previously reported and that a leak of water was 50 percent more radioactive than initially announced.

For the third time in three days, Tokyo Electric Power apologized for delays and errors in announcing the extent of damage at the plant in this northwestern coastal city, which was struck Monday by a magnitude 6.8 earthquake. The company also said that tremors had tipped over “several hundred” barrels of radioactive waste, not 100 as it reported Tuesday, and that the lids had opened on “a few dozen” of those barrels.

Tokyo Electric said it had found some 50 problems at the plant caused by the earthquake, including loose exhaust ducts and damaged pipes. In a statement, the company said it had miscalculated the level of radioactivity of the leaked water, 317 gallons of which flowed into the Sea of Japan. However, it said the water’s level of radioactivity was still far too low to harm the environment.

Television scenes showed Tokyo Electric’s president, Tsunehisa Katsumata, bowing low in apology during a visit to the area on Wednesday. “We will start an investigation from the ground up,” he pledged.

The company’s slow pace in revealing the plant’s problems has brought criticism from Japanese all the way up to the prime minister and fed public fears about the safety of nuclear power. On Wednesday, the mayor of Kashiwazaki, Hiroshi Aida, chimed in, ordering the plant to stop operations until safety could be ensured.

The troubles at the plant raise questions about nuclear power at a time when resource-poor Japan must compete for oil and gas with hungry neighbors like China and India. Japan has embraced nuclear power as an alternative to energy imports from the Middle East, but revelations that Monday’s earthquake exceeded the Kashiwazaki plant’s design limits raised concerns about reactor safety in this earthquake-prone country.

Also on Wednesday, the death toll from the earthquake rose to 10 after the body of a 76-year-old man was found near a collapsed Buddhist temple. City officials said they did not expect the count to rise much higher, as most of the city’s 93,500 residents had been accounted for.

City officials said some 9,000 people remained in refugee shelters, though many are expected to return to their homes after the city fully restores electricity on Wednesday. Water and natural gas supplies remain severed.

On Wednesday, many of Kashiwazaki’s streets remained blocked by toppled houses, and major roads had buckled and cracked from the force of the earthquake.

In the city’s center, entire rows of shops had collapsed, and a large karaoke entertainment center leaned precariously over a street. The owner of a photography shop, Akio Yoshino, 53, said the earthquake had been strong enough to scatter heavy glass display shelves across his store like “pieces spilled from a chess board.”

“If I had not been outside having a cigarette just at that moment, I’d be dead now,” he joked dryly, as his hands visibly shook. “Smoking saved my life.”

The earthquake also made itself felt on Japan’s car industry. Toyota announced Wednesday that it would temporarily halt production at domestic plants later this week because the earthquake had destroyed the Kashiwazaki factory of Riken Corporation, a supplier of piston rings.