The mishap took place at Tongseng village, about 140 km from Shillong, Khliehriat Sub-Divisional Police Officer Willy Muksor said.
"All the seven died on the spot. Those killed include two women and a minor girl, while the injured include the driver and two minors (a boy and a girl)," Muksor told IANS by phone from Khliehriat.
He said the vehicle carrying two staffers of Barak Valley Cement Limited (BVCL) and their family members was on way to Guwahati, in Assam, from the cement plant located in Assam's Karimganj district.
BVCL liaison officer S. Chakraborty confirmed those killed include Sanjay Jha, the chief chemist, and Santosh Kumar Jha, the head clerk of the cement plant purchasing unit.
"Our staffers with their family had left this morning to Guwahati to board a train to their native village in Bihar," Chakraborty said.
Of the three injured, two were the children of Sanjay Jha, he said.
"We are retrieving the bodies," Muksor said, adding that the injured have been admitted to a nearby hospital.