Police are investigating following a serious crash near Goulburn today.

About 12.40pm (Monday 13 June 2016), emergency services were called to The Hume Highway Bypass, south of Goulburn, following reports of a single-vehicle crash.

Police have been told a Toyota Land Cruiser towing a caravan was travelling south when it hit a guardrail and rolled.

The four occupants of the Toyota – the male driver, female passenger and two boys – aged six-weeks-old and four – were injured.

The female passenger sustained serious injuries and was airlifted to Canberra Hospital.

The six-week-old boy was taken to Canberra Hospital by NSW Ambulance Paramedics in a serious but stable condition.

The male driver and four-year-old boy received minor injuries and were treated at the scene.

All southbound lanes on the Hume Highway are closed while police from the Crash Investigation Unit conduct inquiries into the incident.

Traffic diversions are in place.