(Xinhua)
Updated: 2008-03-04 15:16

BEIJING - The death toll from the explosion of a pump at a sewage plant in Gaobeidian in eastern Beijing has risen to four.

More than 20 on-site workers were poisoned by gas leaked from the explosion on Monday at 11 am. The explosion was in an underground pump connected to four sewage tanks, according to the municipal work safety authority.

Chaoyang Hospital in Beijing treated 23 workers from the plant. Two died before they reached hospital, and one died during emergency treatment, said Li Chunsheng, head of the hospital's emergency treatment department.

The fourth death was at the Civil Aviation General Hospital which admitted one worker after the accident on Monday.

"Five workers have left hospital after medical check-up and brief medication. At present, 15 workers are still in hospital for further treatment," said Hao Fengtong, a doctor in charge of the occupational diseases and toxicosis department in Chaoyang Hospital.

Doctors said that the workers' symptoms suggested that they were mainly poisoned by sulphurated hydrogen. But the sewage plant explosion could also produce other deadly gases such as methane.

The cause of the explosion is still under investigation. The workers were unable to account for what happened.