MELBOURNE, Australia (AP) — A man and boy were critically injured and another boy had his surfboard bitten during three separate shark attacks in Sydney in just over 24 hours, police said on Monday.

A surfer in his 20s was bitten on a leg by a shark off North Steyne Beach on the Pacific Ocean coast in the northern suburb of Manly at 6:20 p.m. local time Monday, a police statement said.

Bystanders pulled him from the water before an ambulance took him to a hospital in a critical condition, police said.

On Sunday, a 12-year-old boy suffered serious injuries to both legs after jumping from a six-meter (20-foot) high ledge known as Jump Rock, near Shark Beach inside Sydney Harbor in the eastern suburb of Vaucluse. Police have credited the boy’s three friends with saving his life by jumping from the cliff during the attack and dragging him back to shore.

“The actions of his mates who have gone into the water to pull him out have been nothing but brave,” Supt. Joseph McNulty told reporters.

“Those actions of those young men are brave under the circumstances and very confronting injuries for those boys to see,” McNulty added.

News media have reported that the boy lost both legs in the attack.

Around noon on Monday, an 11-year-old boy was on a surfboard that was attacked by a shark at Dee Why Beach, an ocean beach north of Manly. The shark bit off a chunk of the board, but the boy escaped uninjured.

Local authorities said Sydney’s northern beaches, including North Steyne and Dee Why, would remain closed until further notice.

All three beaches near where the attacks occurred have some form of shark protection netting. It was not immediately clear where the attacks occurred in relation to that netting.

Authorities suspect bull sharks are responsible for at least the first two attacks.

Police had warned after the first attack that recent heavy rain over Sydney had increased the amount of fresh and murky water inside the harbor, heightening the bull shark danger.

Dee Why Beach is close to Ocean Reef Beach where a 57-year-old surfer was killed by a suspected white shark last September.

In November, a 25-year-old Swiss tourist was killed and her partner was seriously injured trying to save her as they swam off a national park north of Sydney.