More than 1,000 local residents were evacuated from their homes in Guangyuan, Sichuan Province, Monday night after a liquid chlorine tank sprang a leak at a swimming pool, poisoning several people with dangerous chlorine gas.

The police make great effort to clear the poisonous gas.

The tank contained 250 kilograms of liquefied chlorine, used to sterilize the swimming pool at East Hill Park in the Lizhou district.

The cause of the chlorine leak was not immediately identified, but the accident posed a serious health risk to local residents, China News Service reported Tuesday.

The gas odor sent several people to hospitals complaining of coughs and stinging eyes.

Police used loudspeakers to order neighbors who lived near the swimming pool to leave their homes.

Local officers blocked an access road to prevent people from entering the hazardous area, the report said.

In an effort to clear the poisonous gas, the police dumped more than 250 kilograms of caustic soda into the swimming pool to neutralize the concentration of chlorine.

The police also sank the chlorine tank under water to purge remaining traces of the chemical.

The emergency was declared under control at 5:30 am Tuesday after seven hours of rescue work, and officials from the local department of environmental protection declared that the air was safe to breathe, according to the report.

More than 120 medical workers were deployed to the scene to help with the hazardous cleanup.

Chlorine is a lethal gas that can be used to kill bacteria and viruses in both swimming pool and tap water.

Chlorine gas can destroy the respiratory system in human beings and an airborne concentration of more than 3,000 cubic meters can cause the heart to stop beating.

Qian Zhi, a local high school student, told the Global Times Tuesday that he breathed in some of the acrid fumes before police ordered him to leave his house.

"I felt dizzy and sick after breathing in the smelly gas," Qian said. "I don't know whether I was poisoned or it was just a kind of psychological reaction."

Qian said that he spent a sleepless night at a cyber bar far away from the swimming pool.

A local resident surnamed Wang told the Global Times that both her grandfather and aunt who lived near the swimming pool were safe after they left their houses and lodged with relatives on Monday night.

An employee surnamed Qiu at the publicity department of Guangyuan told the Global Times Tuesday that he did not know the details of the accident.

Another case of chlorine poisoning occurred on the same day at a swimming pool in Nanjing, Jiangsu Province.

As many as 23 swimmers suffered abnormal symptoms, including vomiting and coughing fits on Monday afternoon after they inhaled noxious fumes while swimming, Modern Express reported.