In Sydney, Australia, a series of shark attacks over a span of just 24 hours has left a man and a boy critically injured, while another boy experienced a close encounter when his surfboard was bitten, according to police reports on Monday.

On Monday evening, a surfer in his 20s was attacked by a shark while off the coast of North Steyne Beach in Manly, a northern suburb of Sydney. The attack occurred at 6:20 p.m. local time, and the man suffered significant leg injuries. Onlookers quickly pulled him from the ocean, and he was transported to the hospital in critical condition.

The previous day, a 12-year-old boy sustained severe injuries to both legs after leaping from a six-meter (20-foot) ledge known as Jump Rock, located near Shark Beach in Sydney Harbor’s eastern suburb of Vaucluse. The boy’s quick-thinking friends, who jumped into the water to rescue him, have been praised for their courageous actions that likely saved his life.

“The bravery displayed by his friends, who immediately went into the water to rescue him, is truly commendable,” Superintendent Joseph McNulty remarked to the press.

“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.