The MSRTC bus, coming from Jawhar taluka towards Thane city, hit the tanker from behind last evening near Lodha complex, they said.
The tanker was coming from Bhiwandi towards Thane city, police said.
The two seriously injured passengers were being treated at Thane civil hospital while the other victims were allowed to go after being provided primary treatment.
The driver of the Maharashtra State Road Transport Corporation (MSRTC) bus, identified as Sadashiv Patil (30), has been arrested.
He has been booked sections 279 (rash driving or riding on a public way), 337, 338 (causing grievous hurt by act endangering life or personal safety of others) of the IPC and section 184 of the Motor Vehicle Act, police added.
The Kapurbawdi police are investigating the matter.