The accident took place in the evening near Chhaila Bazar when a Tempo Traveller, with 13 passengers who were to attend a marriage, was headed towards Rohru.
The reason behind the mishap was not immediately clear.
The deceased have been identified as Nitya Nand Bhardwaj -- the younger brother of state education minister Suresh Bhardwaj, Anil, and Kewal, Shimla Superintendent of Police Omapati Jamwal said, adding that all were residents of Kasumpti.
The injured have been shifted to Theog Hospital, they said.
(With inputs from agencies.)