A multi-vehicle accident on the southbound lanes of the NJ Turnpike killed 3 people from Georgia and left parts of the roadway shuttered for hours, leading to heavy backups and congestion.

Lt. Stephen Jones says police are still investigating what caused a tractor-trailer to hit the back of a Toyota Camry around 10 a.m. Thursday below Exit 5 near Mount Laurel.

Three people and a dog in a silver Toyota Camry died, and the occupants are believed to all be from Stone Mountain Georgia. Jones says the Camry's 51-year-old male driver, a 49-year-old female and a 12-year-old male were all pronounced dead at the scene. An 18-year-old woman from the same car was treated for minor injuries at Cooper Hospital.

Jones says a second car was involved in a minor way, and a second tractor-trailer swerved to avoid the accident. The occupants of both tractor trailer trucks were uninjured, and another driver of a Ford Edge was also unharmed.

All southbound lanes of the NJ Turnpike have been re-opened following the crash.

(The Associated Press contributed to this report)