A tragedy in Sydney’s southwest might have been avoided if a scooter rider had been wearing a helmet.

Police say a 44-year-old man was riding the scooter without a helmet in the suburb of Wilton about 11pm on Saturday when it clipped the gutter, pitching him to the ground.

The man suffered a serious head injury, with friends and family conducting CPR until NSW Ambulance paramedics arrived.

He was taken to Campbelltown Hospital in a critical condition but died overnight, police said on Sunday.

An investigation has been launched into the circumstances of the crash and a report will be prepared for the coroner.

-AAP