Firefighters have extinguished a bus fire that closed the Sydney Harbour Bridge in peak hour, but traffic chaos is continuing.

Motorists are still advised to avoid the area where possible, with all approaches congested.

The Sydney Harbour Tunnel and Anzac Bridges have borne the brunt of traffic seeking alternate routes, with both heavily congested.

One northbound lane has reopened, however buses are not being allowed through.

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Northbound bus commuters have been advised to catch a train across the bridge, where possible.

Many bus services are terminating at, or linking in, to train stations.

A Transport Management Centre spokeswoman said congestion was at chokepoint in both directions.

"If you are heading into the city, we advise you catch the North Shore line train or ferry," she said.

"The bridge had been closed in both directions, and that is changing as the clean up continues. "One north bound lane is open but we are still advising people to stay away.

"Given you usually have four lanes, traffic is incredibly heavy."

The flames take hold. Photo / Alex Mullane / Twitter
The flames take hold. Photo / Alex Mullane / Twitter

Firefighters were called to Milsons Point just before 5.30pm, after the bus burst into flames.

The cause of the blaze is yet to be determined.

The 30 passengers on board made it safely off the bus, however, a New South Wales Ambulance Service said three were treated for minor smoke inhalation.

All three were taken to Royal North Shore Hospital for further treatment.

A Fire and Rescue NSW spokesman said four fire crews were called to the scene but had trouble getting to the bus due to the traffic congestion the incident had caused.

He said the fire was extinguished soon after they arrived on scene and the burnt wreckage had since been removed.

A small amount of oil remains on the roadway and requires further clean-up, he said.


Passengers had to be evacuated and left the bridge on foot before firefighters arrived to extinguish the blaze at 5.35pm, The Daily Telegraph reported.

"A couple of guys tried to put it out with fire extinguishers but had no hope," one commuter on the bridge said.

"The flames were getting bigger and bigger."