Rescuers have freed a teenage driver who became trapped when a truck and several vehicles crashed, causing traffic chaos on a major NSW road on Thursday.

A truck crashed into two vehicles on the Hawkesbury River Bridge, on the Pacific Motorway at Mooney Mooney, on Sydney’s Central Coast, about 7.15am.

One of the vehicles caught fire, NSW Ambulance told 7NEWS.com.au.

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The male truck driver in his late teens was trapped for more than an hour-and-a-half.

He is understood to have suffered multiple lower leg injuries.

He will be airlifted to Royal North Shore Hospital.

All southbound lanes heading into the city on the M1 have been closed.

One of three northbound lanes is also closed.

Traffic is building up behind the crash for about 5km, all the way to Mount White, Sunrise understands.

Emergency services are working to clear the wreckage, with a helicopter, tow truck, and Transport for NSW also at the scene.

Motorists are urged to avoid the area and prepare for significant delays.

To use the Pacific Hwy, traffic is being diverted through the exit at the Mount White interchange.

“This diversion is suitable for light vehicles only. Heavy vehicles are being parked,” Live Traffic NSW said.