At about 10.50am yesterday a silver Honda sedan and a semi-trailer collided in the southbound lanes of the Hume Highway about 20km north of Yass.

Four people, believed to be travelling in the Honda have died, while the semi trailer driver, a man aged in his 50s, was treated for head and leg injuries at Yass Hospital.

Police established a crime scene and will prepare a report for the NSW Coroner.

Meanwhile, the southbound lanes of the Hume Highway remain blocked for most of the day while police conducted an investigation into the circumstances surrounding the collision.

Local diversions were in place, and police directed motorists to take alternate routes.

Anyone with information about the circumstances surrounding the incident is asked to contact Yass Police or Crime Stoppers on 1800 333 000.