A wobbegong has been identified as the species of shark that bit a Sydney surfer on Sydney's northern beaches this week.

A wobbegong shark bit a surfer at Manly. Credit:Nick Moir

The 28-year-old man was bitten on the foot at Manly just before 7pm on Wednesday, prompting a shark alarm to be sounded at the popular beach.

A shark biologist had assessed photographs of the wounds and identifed the culprit as a wobbegong shark, the Department of Primary Industries said on Friday.

The brown-coloured fish, also known as a carpet shark, can grow up to three metres long, inhabit shallow inshore waters and can become aggressive if disturbed.