The accident occurred at Lohali near Kakarighat in this district when the bus, which was returning to Kotdwar from Bageshwar, was hit by the boulder, SSP Nainital Janmejay Khanduri said.
The deceased were pilgrims who were on their way back to Kotdwar after visiting the Bageshwar temple, he said.
Khanduri, who supervised the rescue operations, said that due to the ongoing work to expand the road network in the area combined with the seasonal rains, such a tragedy had taken place.