Eight steel workers were confirmed dead on arrival to hospital Monday in Dalian, a coastal city in northeastern China's Liaoning province, local work safety watchdog said Tuesday morning.

According to Yang Jikui, head of the city's work safety bureau, the eight workers fainted suddenly at around 4:45 p.m. Monday when they were repairing an electrical device in a small underground pump workshop in the No. 1 steel plant of Dalian Special Steel Co. Ltd., affiliated to the Dongbei Special Steel Group.

Yang said preliminary blood tests showed no sign the victims had been electrocuted, but there were signs of carbon monoxide and other unidentified gases in the blood.

However, according to doctors the workers could have died of serious oxygen deficiency, as the 1.45-m-deep underground workshop had a floor space of only a dozen square meters or so and had been closed for a long period of time.

Yang said experts would try to ascertain the cause of deaths after autopsy Tuesday.