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A woman is dead and another is fighting for her life after a head-on crash on Sydney's Harbour Bridge.

The fatal crash involving a red Mitsubishi Mirage travelling north and a BMW travelling south happened at 7.15am on Thursday. 

The driver of the  Mitsubishi Mirage died at the scene. 

Her two passengers – both men believed to be aged in their 30s - suffered head injuries, they have been taken to Royal Prince Alfred Hospital via rescue helicopter.

Emergency teams had to free the driver of the BMW – a woman believed to be aged in her 40s – who was trapped in the car.

The carnage during peak hour brought the city to a standstill with massive queues of traffic stretching in both directions. 

The bridge has now been closed and motorists are being encouraged to work from home. 

A witness, who had been on a bus heading into the city at the time, described the scene as 'chaotic' as footage showed dozens of rescuers trying to free the trapped motorist.

Emergency teams had to free the driver of the BMW – a woman believed to be aged in her 40s – who was trapped in the car

The bridge was closed for a few hours while emergency crews treated the patients before they cleared the scene

She said it looked as though the black BMW x4 had been 'completely destroyed'.

'I saw the whole roof of the black car had been sliced off, there were still people in the car, it looked they were trying to get them out,' she told Daily Mail Australia

'There was also a stretcher on the side of the road and there was a blanket over someone.' 

Initial reports suggest speed may have been a factor in the crash.

Horrific scenes on Sydney Harbour Bridge as emergency crews swarm the road after a fatal crash on Thursday morning

A Mitsubishi Mirage travelling north and a BMW travelling south collided on the Sydney Harbour Bridge on Thursday morning 

A woman is dead and another is trapped in her car after a head-on car crash on Sydney's Harbour Bridge on Thursday (pictured: fire crews at the scene)

The crash has caused massive delays during the morning commute with hundreds of cars backed-up along the bridge (pictured is a helicopter arriving at the scene)

Fire crews and paramedics surround a car involved in a fatal crash in Sydney on Thursday, a woman in her 40s is still trapped inside

NSW police are at the scene investigating the cause of the crash.

The collision has caused massive delays during the morning commute with hundreds of cars backed-up along the bridge. 

Massive queues of traffic were seen before cars were diverted by police.

Fire fighters were forced to head to the scene on foot from The Rocks Fire Station because of the traffic chaos. 

The crash has sparked chaos during the morning commute with hundreds of cars backed-up along the bridge

A helicopter is at the scene to assist with transporting patients to hospital, gridlock traffic caused issues for emergency teams

Motorists are being asked to avoid the area and are being advised to use the Sydney Harbour Tunnel instead during this time. 

Secretary of the Police Association of NSW Pat Gooley has urged drivers stuck in traffic to stop making U-turns.

'What we do have is people doing U-turns, and we have emergency services trying to make their way on the other side of the road,' he said.

'People have to stop doing these U-turns, it's too dangerous.'  

The head-on crash, which happened shortly before 7.30am on Thursday, has caused commuter chaos with massive queues of traffic

All northbound lanes was closed and three out of five southbound lanes were also closed when the crash happened, authorities have now shut the entire bridge