Three shark attacks have rocked Sydney, Australia, in a 24-hour period ... leaving one boy fighting for his life after losing both his legs to the jaws of one of the ocean predators, and a man in critical condition after his leg was bitten in the water.

The boy was attacked after jumping off a rock ledge into the ocean near Sydney Sunday ... after the 12-year-old boy was bitten, some of his friends jumped in after him and swam him back to shore.

Then on Monday, an 11-year-old surfer narrowly missed serious injury when a shark took a giant bite out of his surfboard.

But later Monday, a surfer in his 20s was critically injured when a shark bit one of his legs, News Corp Australia reports. Rescuers performed first-aid on the beach before he was hospitalized.

Watch the video ... you can see beachgoers rushing to his aid to pull him out of the water.

The 11-year-old boy had been thrown off his own surfboard when a shark chomped on it multiple times, taking out a chunk of it.

The U.S. Sun reports the boy's father rescued him after hearing his screams for help.

The attacks occurred despite safety netting at each of the locations, according to ABC News. All of Sydney’s northern beaches have been closed by authorities.