The pickup truck was carrying about 20 passengers. It seemed one of its tyres burst, sending it out of control. It hit a tree and then flipped over into a ditch in Nong Yai district in Chon Buri province early Friday morning, Pol Col Somneuk Haanta said.
Five of the passengers died on the spot and two more died in a hospital, he said. Seven others were hurt.
Police were trying to find the driver, a Thai, who fled the scene.
Earlier this month, nine Cambodians on their way home for Songkran died in a passenger van crash in Chanthaburi province.
Thailand has more than a million migrant workers, mostly from Myanmar, Cambodia and Laos.