Drivers have been left stranded for up to four hours in Sydney’s M4 motorway tunnel within the WestConnex, after fears of a concrete roof collapse which saw the closure of all westbound lanes.

About 6am on Thursday morning, Transport for NSW advised the tunnel was closed westbound between Haberfield and North Strathfield due to “emergency roadworks”.

On Thursday afternoon, Transport for NSW coordinator general Howard Collins said Transurban had requested to close the road in the early hours following an overnight inspection.

He said engineers had identified an issue with “shockcrete”, a form of sprayed-on concrete which separates the tunnel from a waterproof membrane and the sandstone above.

“The engineers ... who were working for Transurban last night discovered a couple of large bu

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