The Transport for NSW bus was in the left-hand lane travelling east, just past the intersection with Harris Street, when it caught on fire at around 9.15pm on Thursday night.

Emergency services arrived shortly afterwards.

Photographs from the scene showed firefighters spraying the bus with foam as grey smoke rose from the engine bay.

Two lanes were closed citybound and one lane was closed in the opposite direction to allow the emergency response, a spokeswoman for the Transport Management Centre said.

Traffic was moving in both directions with little congestion, but motorists were advised to drive with caution and allow extra travel time.

Superintendent Adam Dewberry from Fire and Rescue NSW said there were no reports of any injury as a result of the fire.

"We believe the fire originated in the engine compartment," Mr Dewberry said. "Two fire trucks have attended, they've knocked it down.

"I've got reports there was a fair bit of fire at the rear of the bus."

It's not know if the bus was in service or if it had any passengers on board at the time.

The fire is the latest in a series of blazes on buses this year, as the state government comes under pressure to install fire suppression systems on all public and private buses.

In September, all lanes of the Sydney Harbour Bridge were closed when a peak hour bus became engulfed in flames, causing the commuters on board to run to safety.

Another bus caught on fire on the M2 at Beecroft in November, while earlier this month two buses were completely destroyed by fire in the car park at Sydney Airport.

More than 5000 buses in Sydney and NSW are due to be fitted with fire suppression systems, which deploy a high-pressure mist when they detect fire or heat within the engine bay.

Bus on fire, George Street, Sydney<\/p>\n",colour:"green", title:"Bus fire", maxWidth:200, open:0}] ); } if (!window.gmapsLoaders) window.gmapsLoaders = []; window.gmapsLoaders.push(CreateGMapgmap20161122222218); window.gmapsAutoload=true; /*]]>*/ ]]>