The mishap occurred at around 4.30 AM when the private bus skidded off the highway and hit the roadside tree after the driver dozed off, they said.
The deceased were identified as Atul Tawde (35), Suhas Gode (32) and Sandeep Rane (35), police said.
While six out of 22 injured were shifted to Mumbai for treatment, the rest were admitted in hospitals at nearby Pen and Nagothane.