Three crew members were confirmed dead and another six were missing after two dredgers were badly damaged during a gale off north China's Tianjin Municipality, local authorities said Thursday.

Photo taken on April 16, 2009 shows a dredger lies on the beach after being badly damaged during a gale off north China's Tianjin Municipality. Three crew members were confirmed dead and six others were missing after two dredgers were badly damaged on April 16. [Xinhua]

The accident happened at about 5 a.m. Wednesday when the two vessels off a refinery of the Dagang Oilfield with 37 on board were badly damaged in high winds caused a swell of nearly five meters, officials said.

Helicopters and rescuers saved 28. None of them were seriously injured, construction workers at the scene said.

Rescuers are still searching for the missing.

Initial investigation showed the two ships did not obey a warning to return to the port. Gales at speeds of 62 to 75 kilometers per hour broke the rope, officials said.

The dredgers are used to gather sediment and dispose of it outside the waterway to ensure navigability.

Separately, 13 workers from a coastal highway construction site in the city were trapped by sea water at about 7:20 a.m. Wednesday. They waited on top of excavation vehicles until rescue came half an hour later.