At least 14 people were killed on Monday and many more were injured in a stampede during Chhath festival in Patna, police said.
Among the casualties were many children and women, who had come to the banks of the River Ganges in Bihar to enjoy Chhath, the biggest Hindu festival in the state.
Several people were still missing, the police said.
"We have identified 14 bodies so far and we fear the casualty figures may go up," a senior police official told journalists.
He said the stampede had been triggered by the collapse of a makeshift bamboo bridge built along the banks of the river and appealed to the public to keep calm.
Devotees had gathered along the river to offer prayers to the setting Sun.
The injured, several of whom were said to be in critical condition, were taken to hospital in Patna.