Six people were killed and one was injured in a freeway accident involving three vehicles in east China's Shanghai early Saturday morning, Shanghai police said.

The accident happened at 5:23am when a truck rear-ended a passenger car and then a semi-trailer on the Shenyang-Haikou Expressway, according to the city's public security bureau.

Five people aboard the car and one from the truck were killed. Another person from the truck was injured but not in life-threatening condition.

Police said the cause of the accident is still under investigation.