KASHIWAZAKI, Japan – Failure to follow procedure was to blame for the latest leak from a nuclear power plant damaged in this week’s earthquake in northwestern Japan, a top government official said Friday.

Tokyo Electric Power Co. said radioactive material was leaking from an exhaust vent as late as Wednesday night, two days after the plant suffered a near-direct hit by Monday’s quake, which killed 10 people and injured more than 1,000.

TEPCO announced Friday that a check the previous night at the plant, 135 miles northwest of Tokyo, confirmed the vent leak had stopped.

The embattled operator of the Kashiwazaki-Kariwa plant _ the world’s largest in terms of capacity _ already had announced a barrage of leaks and malfunctions, and said the latest might have been caused by workers failing to follow rules and turn off a fan inside the building.

Chief Cabinet Secretary Yasuhisa Shiozaki said the trade and industry minister would issue a further “stern warning” to TEPCO.

“This is an error of not implementing the manual,” Shiozaki said when questioned about the latest exhaust vent leak.

TEPCO and nuclear regulators have stressed the amounts of radioactivity leaked were extremely low and posed no threat to the environment or local residents. The announcement of the leak came a day after officials issued similar assurances about other damage at the plant _ including a fire, burst pipes and waste spillage.

The seven reactors at the Kashiwazaki-Kariwa plant shut down automatically when the quake hit, and the plant has been ordered closed indefinitely while inspections and repairs are carried out to assure it can be restarted safely.

TEPCO has warned the closure of the key nuclear reactor could trigger a power shortage in the summer months. The Tokyo-based company has asked six other power companies in Japan to consider providing emergency electricity to prepare for a surge in demand as people turn up their air conditioners in the summer heat.

All six companies said they would cooperate in providing power and TEPCO is also considering restarting oil and gas plants, TEPCO officials said late Thursday.

The government has urged the operators of Japan’s 55 nuclear reactors _ which supply one-third of Japan’s energy _ to speed up safety checks for earthquake resistance, a top concern in the temblor-prone nation.

Officials at the Kashiwazaki plant acknowledged they had not foreseen such a powerful quake hitting the facility. They also repeatedly underreported its impact after it hit.

After initially saying the quake had caused 50 separate types of minor damage or leaks, TEPCO upped that estimate to 63.

Associated Press writer Kana Inagaki in Tokyo contributed to this report.

A service of the Associated Press(AP)