Police were called at 6.45am following reports of a crash during heavy rain on the Barton Highway, near Casuarina Lane, at Jeir, about 30km south-east of Yass, just north of the ACT.
Officers found a Ford Ranger utility and a Mitsubishi Triton utility had collided.
The female driver and male passenger of the Mitsubishi, and a male driver and male passenger in the Ford died at the scene.
They have not been formally identified.
Another male passenger in the Ford has been treated on scene by paramedics and is being taken to hospital.
Their ages are not known at this time.
The Barton Highway is closed in both directions.
Firefighters are working to cut survivors trapped in the wreckage of the vehicles.
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Southbound traffic on the Barton Highway is being diverted via Murrumbateman Road and Sutton Road to join the Federal Highway.
Northbound traffic on the Barton Highway is being diverted back to Canberra and should use the Federal Highway instead.
These diversions are suitable for all vehicles.
Motorists should allow plenty of extra travel time and follow the directions of emergency services and traffic crews on scene.
There is no forecast for when the highway will reopen.
For the latest traffic information, visit www.livetraffic.com or download the Live Traffic NSW app.
Police have begun inquiries.
Anyone with dashcam vision or further information is urged to call Crime Stoppers on 1800 333 000.
This is a developing story … More to come.
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