At least 25 members of a wedding party were killed when their bus plunged into a small river in India's north-eastern state of Assam, police said.
The bus was travelling from the state capital, Guwahati, to Kamrup district.
The incident happened when a wooden bridge that the bus was crossing collapsed and fell into the water.
Local villagers rushed to the accident site at Rajabari after the accident on Monday night and rescued six passengers from the wreckage, reports said.
The bus was reported to be carrying about 40 passengers.
Police divers arrived at the site, where many villagers had gathered, on Tuesday morning to begin the search for the missing passengers.
Bus crashes are common in India. Often caused by poorly maintained vehicles and reckless driving, they claim thousands of lives every year.