Traffic chaos after 11-vehicle crash on F3

Motorists are being urged to avoid the Hawkesbury River Bridge after an 11-vehicle crash north of Sydney.

Paramedics are treating a number of motorists after an 11-vehicle pile-up that is causing traffic chaos north of Sydney.

The F3 freeway has now reopened in both directions following the accident that happened about 6.30am (AEST).

But southbound traffic queues stretch for about five kilometres near the Hawkesbury River Bridge, the Transport Management Centre says.

Paramedics are treating at least two motorists, an Ambulance NSW spokeswoman told AAP.