At least 20 people died and 13 were injured when a bus plunged into the swollen waters of a river in northern Uganda, police officials said Wednesday.

The bus, which was carrying 35 passengers, swerved off a bridge over the River Aswa, north of the region's main town of Gulu, on Tuesday night.

"The bus was loaded with people when it fell into the river," Deputy Police Spokesman Samson Lubega told Deutsche Presse-Agentur dpa.

"Thirteen people escaped with injuries. Others died and some of the bodies are in the wreckage, which is still under water," Lubega added. The cause of the accident was still unknown.