The bus carrying a total of 38 passengers was on its way from Thane to Ahmednagar when it fell into the 400-feet Malshej ravines near Tokawade in the morning, an officer in the disaster control management room said.
"As per initial information available with me, a truck collided with the Maharashtra State Road Transport bus, knocking it down the valley," Maharashtra State Road Transport General Manager (Traffic) Suryakant Ambawdekar said.
20 bodies are kept at Ottur village while six bodies are in a hospital at Junnar.
Twelve injured have been admitted to hospitals in and around Thane and Pune, control room sources said.
District Disaster Control Officer Jaideep Visave said "the district headquarters got the message around at 10.30 am and a team comprising police personnel, medical attendants and rescue workers was rushed to the spot.
Murbad Tehsildar Prashant Joshi said many of the injured comprised women and help had been sought from trekkers to retrieve injured people from the valley.
Malshej Ghat is a famous picnic spot located in the Sahyadri mountain ranges, located on the border of Thane and Ahmednagar districts.