Image: Nine News

An overheight truck is causing traffic chaos after clipping a bridge on the M4 motorway in Sydney’s west.

Two of three citybound lanes have been closed throughout the morning after the truck’s crane struck the Bennett Road overpass at Colyton.

Traffic is banked back about 10 kilometres with motorists being diverted onto the Great Western Highway, via the Northern Road exit.

Emergency services along with RMS Bridge Engineers are currently assessing the damage.

NSW Police Traffic and Highway Patrol Chief Inspector Phil Brooks tells Ray Hadley how the incident occurred.

“He was just dropping off form work on the M4 for the construction there.

“He’s done one drop 150 metres before that overpass. He’s then gone ahead without retracting the arm and struck that bridge.

“The Nepean Highway Patrol will be taking action for what is a critical breach, and court attendance notices will be issued to that driver.

“It’s not good enough.”

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For traffic information, go to livetraffic.com