There’s chaos on the M1 motorway north of Sydney this morning due to debris on the road.

Dozens of cars have suffered punctured tyres after hitting the metal debris on the southbound side of the road at Calga.

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The middle lane is closed, just past Mooney Mooney Creek Bridge and traffic is queued around 7km.

Police say the debris is the result of three large sheets of metal fencing falling off an unidentified vehicle.

They are appealing to the public to help identify the vehicle, which was travelling south on the M1 just after 5am.

Listener Maury phoned Alan Jones saying, “there would be at least 15 to 20 cars on the side of the road”.

“I was trying to focus on the road, there was that much confusion going on in the area.

“The amount of tow truck vehicles, flashing lights and all the cars pulled over in the breakdown lane with flat tyres, trying to jack them up and replace the tyres.”

Click PLAY below to hear Maury’s call

Motorists can divert onto the old Pacific Highway instead.

Emergency services, traffic crews, tow trucks and a street sweeper are on site working to clear the debris as quickly as possible.

CALGA: Southbound traffic is heavy on the M1 Pacific Mwy due to metal debris on the road. Slow down and exercise caution.

— Live Traffic NSW (@LiveTrafficNSW) March 18, 2019