It happened around 10:30 on Wednesday morning at Lovers Point Beach.
Police say the swimmer is suffering from significant injuries - footage shows surfers and paddleboarders racing over to help the man.
They pulled him to the beach and then the victim was taken to the hospital.
The beach at Lovers Point and Sea Palm turnout is now closed until Saturday as an aerial search for the shark continues.
The area is being close monitored for any additional sightings.