Twelve people have died and at least 20 others are missing, feared drowned, after an overcrowded boat jammed with Hindu pilgrims capsized in a river in southern India.

The accident occurred as the boat was crossing the Godavari River in Andhra Pradesh state, police superintendent Madhava Chary told AFP from West Godavari district, 500km from state capital Hyderabad.

About 50 passengers were on the boat, which capsized early in the morning and had the capacity to carry 35 passengers, police said.

Rescue vessels and divers were dispatched to search for missing passengers, most of whom hailed from nearby villages.

Relatives of victims anxiously waited for news on the river banks and angrily confronted government officials who had come to inspect the scene of the disaster.

The ramshackle boat was filled with Hindu pilgrims, including many women and children, on their way to a temple to offer prayers to mark the full moon day of Purnima.

Villagers often travel in poorly built boats to cross the Godavari River, which empties into the Bay of Bengal.