Hero paramedic tells of jet-ski tragedy

Floral tributes have been laid at the scene of a horror jet-ski crash in Sydney's south which killed a 15-year-old boy and seriously injured a 14-year-old boy.

Mitchell Irvine was killed and his friend Noah Watkins was left with a severed arm after they were thrown from a jet-ski on the Georges River at 6pm last night.

Police said the two teenage boys were both experienced riders and both had life jackets on at the time.

Mitchell Irvine (right) was killed and his friend Noah Watkins (left) was left with a severed arm.

A police officer and paramedic swam 50 metres to save Noah as the 14-year-old slipped in and out of consciousness.

Responding officer Constable Jesse Hockey said his response was "instinctive".

"Just got in the water and got it done," Hockey said.

"It was cold, murky and dark - we just swam to where the light was.

"The boy was floating, we grabbed him and pulled him in."

NSW Ambulance paramedic Scott McNamara said the boy's condition deteriorated.

Police retrieved part of the jet-ski as they continue with their investigations.

"We just got him to shore as quickly as we could," McNamara said.

"To have saved that young guy, that's why we do what we do."

A short time later Mitchell was found in the water but he could not be revived.

Police spent the day at the scene at Tom Uglys Bridge in Sylvania, focusing their attention on what could have caused the crash.

Friends of the two boys laid flowers at the scene for their friend and wished Noah a smooth recovery as he underwent surgery at the Sydney Children's hospital.

"Fly high," one person wrote online, while another said "always loving you" with an emoji of a broken heart.

"This boy was the most purest boy you could ever meet," another person said.

"Forever 15, love yah Mitch … Hope for a speedy recovery Noah," said another.

Floral tributes have been laid at the scene of the horror jet-ski crash.

Police spent the day at the scene at Tom Uglys Bridge in Sylvania.

Police retrieved part of the jet-ski as they continue with their investigations.

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