One person has been seriously injured after a vehicle flipped on the Southern Motorway during a crash between a car and a truck.

Police said they are responding to the crash on the Southern Motorway, in the northbound lanes near the Papakura on-ramp.

The incident has closed two of the lanes, which had caused congestion to build.

Police confirmed the crash involved a car and a truck and was reported at 10.50am.

A motorist who drove past the accident said she saw a “smashed up” vehicle flipped on its side.

Six police cars were at the scene, and police were investigating the circumstances of the accident, she said.

Traffic was heavily congested in the area, she told the Herald.

Police advised motorists to expect delays and asked them to avoid the area if possible.

Hato Hone St John told the Herald they responded with one ambulance and one rapid response vehicle.

“Three patients were assessed at the scene, with one of those transported to Middlemore Hospital (by ambulance) in a serious condition,” the St John spokesperson said.

St John said the other two people were in minor condition and did not require transportation to hospital.

Police said the Serious Crash Unit will be attending.