BEIJING - Four workers were confirmed dead in an underground work accident on Saturday in Beijing, local authorities said.

The accident happened in Changping District in the morning when seven workers were laying power lines underground. The project is undertaken by a Beijing-based hydroelectric technology company.

These workers were poisoned by gas in the tunnel. Four of them were killed while three others are still being treated in a local hospital.

People who are believed to be responsible for the accident have been controlled by the police.

An investigation into the cause of the accident is under way.