Rescuers search for victims on the Kolohi river

As many as 50 people may have drowned after an overcrowded river boat with engine trouble hit a bridge and capsized in the north-eastern Indian state of Assam, officials say.

Survivors said more than 20 passengers were trapped below deck. Those on board were on their way to a boat race.

The motorised boat sank on the Kolohi river in Kamrup district.

Many of at least 150 passengers on board managed to swim to safety against strong river currents, reports say.

Locals quoted by newspapers said that teams from the National Disaster Rescue Force and State Disaster Rescue Force were only able to reach the scene of the accident three hours after it happened.

The Kolohi is a tributary of the Brahmaputra River, which has been flowing much faster than usual because of recent monsoon rains.

The boat sank in part of the river not far from the city of Guwahati. (BBC)