Police are seeking witnesses to a nasty collision between a cyclist and a runner in Perth’s northern suburbs.

It’s alleged the 45-year-old woman was hit by a man riding an electric bike while she was running on the footpath along the West Coast Highway in Watermans Bay on Tuesday morning.

The woman suffered a broken arm and ribs, and was taken to Sir Charles Gardiner Hospital for treatment.

Police say the cyclist fell to the ground and became aggressive when bystanders came to assist him.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000.