HARBIN - Rescuers had pulled four people out of the debris of a collapsed office building by Monday afternoon in northeast China's Heilongjiang Province. But an unknown number of people may still be buried.

The four people, including two critically injured, have been sent to hospital for emergency treatment, a rescuer said, adding there are no reports of deaths so far.

The rescue operation involving more than 100 rescuers is still underway, with people using life detectors to look for the missing people.

Earlier the rescue team quoted witnesses as saying that five people might have been buried in the accident.

The eastern wing of a 7-year-old office building owned by Jixian County Water Company in the city of Shuangyashan fell apart at about 7:50 a.m. Monday. At the time of the accident, the four-story building was undergoing renovation.