Twelve heavy vessels broke their moorings Saturday and are now being swept down a turbulent river in northeast China, threatening to slam into a major dam on the Songhua River.

Many boats and 300 soldiers were mobilized by 12:30 p.m. to try to stop the vessels before they slam into the Fengman Power Plant dam, Jilin City police said.

The vessels had been swept into the Songhua River from a tributary in Huadian City, Jilin City. The vessels are used for river gold mining and the heaviest one weighs nine tonnes.