The bus was carrying 34 employees of an agriculture university when it plunged off a mountain road while negotiating a curve in Raigad district of Maharashtra state, said civil administrator Vijay Suryawanshi. He said the bus fell into a deep, forested gorge.
One man survived as he jumped out of the bus and later scaled onto the road to inform university officials about the accident, Suryawanshi said.
He said the employees were on a private picnic.
Rescue teams had so far recovered nearly a dozen bodies amid intermittent rains in the area.
India has the world’s deadliest roads, with more than 110,000 people killed annually. Most crashes are blamed on reckless driving, poorly maintained roads and aging vehicles.