The explosion occurred Friday evening at the Tianyuan Chemical Industry Plant in the city of Chongqing, the official Xinhua News Agency said. It said seven people were confirmed dead and two were missing.

At least seven containers of liquefied chlorine were leaking fumes, which could be smelled nearly a quarter-mile away, the report said.

State television attributed the accident to outdated equipment and employees using it incorrectly.

Firefighters were spraying a mix of water and lye into the air in hopes of clearing away some of the gas, Xinhua said.

The leaks were first detected late Thursday, Xinhua said, citing Vice Mayor Zhou Mubing. Minor explosions were heard later that night, but the report didn't mention injuries at that time.

Residents were evacuated from areas within two miles of the plant, Xinhua. Most had returned to their homes by midday Saturday, but 30,000 remained in schools and other government buildings, the agency said.

In December, a gas well leak near Chongqing sent a toxic cloud spreading across villages, killing 243 people in one of China's deadliest reported industrial disasters.

On Wednesday, China's Cabinet accepted the resignation of the chairman of the country's biggest oil producer, which owned the well.

More than 9,000 people were treated for injuries after the disaster and some 60,000 were forced to evacuate.