A 12-year-old boy in Australia is fighting for his life after being attacked by a large shark while swimming in the Sydney Harbour.

The boy and his group of friends were jumping off a six-metre rock ledge at Shark Beach, in the Sydney suburb of Vaucluse, when the attack happened on Sunday.

He sustained critical injuries to both legs and is now under intensive care, authorities say. Police praised his friends for promptly pulling the unconscious boy out of the water before rescuers arrived. It was their actions that gave him a shot at survival, a police superintendent said.

Despite its name, shark attacks are rare at Shark Beach – a popular swimming spot.

“The actions of his mates… have been nothing but brave. [It was] a gallant recovery,” said Joseph McNulty, who leads the state of New South Wales’ marine area command.

“Very confronting injuries for those boys to see, but I suppose that’s mateship.”

New South Wales premier Chris Minns also praised the efforts of the boy’s friends.

“I just want to give a shout out to the young people who were in the water that got the young man… and did everything possible to save his life,” Minns said. “That was a brave thing to do.”

Marine police arrived to a “horrendous scene”, McNulty told reporters. They pulled the boy onto a police speedboat and used tourniquets to try and stop the bleeding from his legs.

They also tried to resuscitate the boy as the boat made its way to an ambulance waiting by a wharf.

Authorities believe the boy was attacked by a bull shark, an aggressive species found in warm, shallow waters. Many experts consider bull sharks among the most dangerous sharks in the world.

McNulty believes heavy rainfall over the weekend and brackish water conditions could have created a “perfect storm environment” for Sunday’s attack.

Rain flushes nutrients into the rivers and oceans which can draw sharks closer to shore.

Australia, which is home to some of the world’s best beaches, is also one of the deadliest places for shark attacks. There were at least five fatal shark attacks in the country last year.