UPDATE: The tunnel was re-opened about 11.30am and those diversions have been lifted “now that repairs have been completed”, NSW Traffic said.

A broken fan inside a tunnel on the M5 has sparked bumper-to-bumper traffic along the major Sydney motorway.

NSW Traffic warned of “significant delays” for commuters travelling towards the city along the motorway had queued back to Henry Lawson Dr in Milperra, Western Sydney, on Wednesday morning.

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The traffic was due to “emergency work” shutting down all access in the main tunnel between Beverly Hills and Mascot.

Toll road operator Transurban specified the issue was discovered “in one of the tunnel’s jet fans during routine maintenance”.

“We sincerely apologise for the delays to motorists and are working to have lanes reopened ahead of this afternoon’s peak,” Transurban said.

“Specialist crews and equipment are now on-site conducting a complex operation to safely remove the fan” which will “not impact the safety or integrity of the tunnel”.

“Safety is, and continues to be, our number one priority. We thank motorists for their patience during the closure.”

NSW Traffic has urged commuters to use detour routes on King Georges, Stoney Creek or Forest Rds and Wickham, West Botany and Marsh Sts.

“However traffic is also heavy on these roads,” NSW Traffic said.

“Alternatively, motorists can continue straight on and use the M8 Tunnel.”