A cyclist has died in hospital two days after being knocked from his bike in a collision with a ute at a Perth roundabout.

Jamie Douglas Kneale, 43, suffered serious head injuries when he fell from his bicycle around 3:00pm on Tuesday in Gosnells, in the city's southern suburbs.

He was taken to hospital in a critical condition, and police said on Thursday he had died overnight.

Mr Kneale collided with the vehicle at the intersection of Dorothy and Hicks streets.

The driver of the ute was not injured and police said he was assisting them with their inquiries.

Anyone who witnessed the incident has been urged to call Crime Stoppers.

Earlier on Tuesday a 69-year-old woman was killed when she was knocked off her bike in Halls Head south of Perth.