A boy has been rushed to hospital after a shark attack in Sydney Harbour.

Police pulled a boy, believed to be aged between 12 and 13, from the water near Nielsen Park, Vaucluse, following reports a shark had him about 4.20pm on Thursday.

Nielsen Park offers swimming at Shark Beach with both netted and unprotected areas.

It’s understood the boy was jumping off rocks at one end of the beach when he was viciously attacked by the shark.

Photos from the scene showed police and paramedics at the Rose Bay West Boat Ramp, about 7km east of the CBD.

The boy was given two medical tourniquets and treated at the scene by NSW Ambulance paramedics and first responders for serious leg injuries.

‘The beach has been closed and swimmers are advised to avoid swimming in the water at this time,’ NSW Police said in a statement.

‘There is no further information available at this time.’

A 12-year-old boy suffered serious leg injuries in a shark attack on Thursday afternoon
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A 12-year-old boy suffered serious leg injuries in a shark attack on Thursday afternoon

Police and paramedics attended the scene at the Rose Bay West Boat Ramp
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Police and paramedics attended the scene at the Rose Bay West Boat Ramp

NSW Police confirmed the boy, 12, suffered serious leg injuries
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NSW Police confirmed the boy, 12, suffered serious leg injuries

It's understood the boy was rock jumping at Shark Beach
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It’s understood the boy was rock jumping at Shark Beach

The boy was airlifted by a Careflight helicopter to Children’s Hospital, Randwick, in a critical condition.

‘Swimmers are advised to avoid entering nearby waters at this time,’ NSW Police said.

‘The injuries are consistent with what is believed to have been a large shark.’