A man is fighting for life after being struck by what's believed to be an e-bike in Sydney's west overnight.

The 65-year-old pedestrian was struck on a walking path near Greenmeadows Crescent in Toongabbie about 9.50pm yesterday.

Emergency services were called to the scene and he was treated by paramedics before being taken to hospital in critical condition.

Police learnt the rider had allegedly left the scene following the crash.

Officers set up a crime to be examined by forensic experts.

One line of inquiry being considered is that they were riding an e-bike.

Anyone with information or dashcam footage is urged to contact Parramatta police or Crime Stoppers on 1800 333 000.

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