Nuclear technicians have found no signs of radiation leaks in nuclear facilities in southwest China's quake zone, but 15 radiation "sources" are still inaccessible, Vice Minister of Environmental Protection Wu Xiaoqing said Friday.

"We did not find any radioactive substance leaks into the environment," Wu told a press conference.

Expert teams sent by the ministry and local environment departments immediately after the quake had thoroughly examined all nuclear facilities in the province, he said.

As of Thursday noon, the experts had identified 50 radiation "sources" and had moved 35 to safe areas, while the locations of the rest had been identified, Wu said.

Three of the 15 remaining sources were buried under rubble while the other 12 were in dangerous buildings that technicians could not yet enter, he said. "At the sites, technicians did not detect any leak."

"We have asked local government to inform us when they plan to clean the rubble."

Environmental departments in other quake-hit provinces have not reported any radiation leaks either after inspections of nuclear facilities.

The ministry ordered all organizations that hold radioactive material to tighten self-monitoring and update reports to environmental authorities, Wu said.

Numerous chemical factories were located in the quake-hit region in Sichuan, posing significant environmental threats, but Wu said no serious accidents have happened yet.

According to Wu, there are more than 100 chemical plants in seven major cities in the quake zone (including the provincial capital, Chengdu) and about 76 percent stopped operations after the quake.

Among the 45 local plants on the list of major environmental risks that are under the state or provincial supervision, 41 percent were affected by the quake.

Inspectors have discovered 38 possible environmental threats and ordered the factories to remedy them as soon as possible, Wu said.