National Disaster Response Force personnel rescuing a passenger after a bus fell into a canal in Sidhi, Madhya Pradesh, on Tuesday.
District Magistrate Ravindra Kumar Choudhary said 50 people were killed when the bus skidded off a bridge and fell into the 9.1m-deep canal after the driver lost control.
There were 57 people in the bus, which was going from Sidhi to Satna.
It was unclear what caused the bus to swerve.
Local media reported the bus was completely submerged and images showed officials in orange life jackets using rescue boats to look for survivors.
Officials said the driver and six others swam to safety.
Local officials stopped the release of water into the canal, which sped up rescue operations by divers and allowed cranes to pull the blue bus out.
The police arrested the driver.