A pump at a sewage plant in Beijing has exploded, killing three workers and causing a toxic gas leak that made at least 16 people ill, state media reported.

The explosion took place in the capital's southwest suburbs yesterday morning, Xinhua news agency reported. Two workers died on their way to hospital and another died there, the report said.

"The cause of the accident is still under investigation. The workers were unable to account for what happened," the report said, without explaining the reason for the delay in the report.

Beijing is in the middle of intense preparations for the Olympic Games, which begin on August 8. City officials have been especially keen to upgrade safety and minimise the accidents that threaten many Chinese worksites.

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