Western Freeway closed after motorcyclist dies in Rockbank crash

Gridlocked traffic is building on a major freeway in Melbourne's west after a motorcyclist died in a crash this morning, prompting all lanes to close.

Emergency services were called to the Western Freeway at Leakes Road in Rockbank, following reports a motorcyclist crashed into a barrier about 11.50am.

The motorcyclist, who is yet to be formally identified, was treated by first responders but died at the scene.

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All outbound lanes of the freeway have been closed before Leakes Road as police investigate the crash.

"The exact circumstances surrounding the incident are yet to be determined and police are speaking with a number of motorists who were in the vicinity of the scene at the time of the crash," a Victoria Police spokesperson said.

VicRoads warned commuters to brace for "significant delays" due to an onslaught of traffic building on the freeway.

Motorists have been advised to exit the Western Freeway at Hopkins Road and use Greigs Road and Leakes Road to then return to the freeway.

"Motorists are advised to allow plenty of extra time for their journeys," VicRoads said.

"The closure is under the control of Victoria Police.

"Outbound lanes of the Western Freeway will open when investigations are complete and it's safe to do so."

Anyone who witnessed the crash or has dashcam footage is urged to contact Crime Stoppers on 1800 333 000.