Eerie footage posted online shows one of the two boys involved in a fatal late-night jet ski crash riding a watercraft at the same spot just weeks ago.

Mitchell Irvine, 15, and his friend Noah, 14, were riding a jet ski in the Georges River when they crashed near Tom Uglys bridge at Sylvania, in Sydney’s south, just after 6pm on Tuesday.

Mitchell died at the scene while Noah severed an arm and was rushed to Sydney Children’s Hospital in a critical condition.

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In recent weeks, Noah shared several videos on Instagram of his jet ski adventures with mates.

Just last month, he posted footage showing him jet skiing through the Georges River and under Tom Uglys bridge.

Another video shows a jet ski rider blasting through a river before the vehicle ends up tangled in mangroves.

A third clip shows two boys riding a boat through a waterway, with its bow lifted in the air.

The alarm was raised on Tuesday night when two girls on the shoreline saw the jet ski wreckage in the water and heard Noah calling out for help.

A police officer rushed into the water and pulled Noah to safety before he was taken to hospital.

Mitchell was later found dead in the water and was unable to be revived.

It is understood Noah’s condition has stabilised overnight.

Police are investigating whether the boys hit an obstacle in the water while riding in the dark.

Tributes have begun to flow online as devastated friends grieve Mitchell’s death and send well wishes to Noah.

One friend described Mitchell as the “purest boy you could ever meet”, who had “many great friendships” with his mates.

“Rest up lad, I’m going to miss you,” another boy wrote.

“Praying for you too Noah. Love you lad.”

“LLM (long live Mitch),” a third post read.

“You will never be forgotten.”

It is understood Mitchell’s distraught relatives were at the river when his body was recovered from the water.

Inspector Timothy Carter described the officers’ actions as “heroic”.

“The police have done their best to try to save these kids’ lives,” he said.

“And it’s, you know, we obviously feel great empathy towards the families.”

Police are examining the scene and investigations continue.