A boy is in a critical condition after being attacked by a shark at a Sydney Harbour beach.

The boy, believed to be about 13, was being treated for “serious” injuries “consistent with what is believed to have been a large shark”, police said.

Emergency services were called to Hermitage Foreshore Walk on Steele Point Road at Vaucluse, near Shark Beach, about 4.20pm.

The child is airlifted to hospital. (Max Mason-Hubers)
The boy was being treated for “serious” injuries. (Nine)

The boy was rescued by water police within minutes of triple zero being called, police said.

“(A) Water Police officer attached two medical tourniquets and was immediately given first aid on board the police vessel Water Police 41 for serious leg injuries before being transported to Rose Bay Wharf, where NSW Ambulance paramedics continued first aid,” NSW Police said in a statement.

“The teen was transported to Children’s Hospital at Randwick in a critical condition.

“Swimmers are advised to avoid entering nearby waters at this time.”

Intensive care paramedics and the Care Flight helicopter were sent to the scene, a NSW Ambulance spokeswoman told 9news.com.au.