At least 13 children died after an overloaded boat capsized in the Ganges River in India's northeastern Bihar state, as passengers were reportedly travelling to attend a religious gathering, officials said on Wednesday.

The boat overturned late Tuesday near Rampur Shyamchand village in Vaishali district. Prime Minister Narendra Modi expressed grief over what he described as a "deeply painful" tragedy.

Local residents rushed to rescue passengers, using mobile phone lights and torches to search the water in the darkness.

"It was dark when we suddenly heard children screaming and crying for help as the boat capsized," villager Ravi Yadav, who joined the rescue effort, told AFP.

"We managed to rescue only three children, using the light from mobile phones and torches, because it was dark," he said.

Another villager, Ramlakhan Rai, said the boat was small and in poor condition, with more passengers aboard than it could safely accommodate.

"It is devastating – a few families have lost all their children," he said.

Six people were reportedly rescued alive, including two children in critical condition, while several others were injured and taken for medical treatment.

Police and the State Disaster Response Force (SDRF) deployed teams to the scene as search operations continued for anyone still missing. Preliminary information indicated that between 15 and 20 people were aboard, although the exact number of passengers and final casualty toll had yet to be officially confirmed.

The state government announced compensation of 400,000 rupees for the family of each deceased person and directed officials to expedite rescue operations and provide medical care to the injured. Authorities are investigating the circumstances of the accident. (ILKHA)