Two children under 10 dead after being pulled from Perth's Swan ...

Two children under 10 have died after they were found floating in the Swan River near Perth's CBD late on Sunday afternoon.

Eight ambulances attended the site at Burswood around 5:25pm, after members of the public saw a boy and a girl in the water.

The incident happened near a children's playground between the Narrows Bridge and the Crown casino complex.

More than a dozen police officers cordoned off the area, where revellers had gathered for New Year's Eve celebrations.

The boy and the girl were taken under lights and sirens to Perth Children's Hospital in a critical condition, but both later passed away.

Officers from WA's Coronial Investigation Squad are conducting an investigation and a report will be prepared for the coroner.

Bulal Walizada witnessed people trying to save the children.(ABC News: Cason Ho)

Bulal Walizada, who was in Burswood with his family to bring in the new year, witnessed the rush as a man jumped into the river to rescue the children.

"He's just rushed over, jumped in, pulled them out of the water," he said.

"There was a woman who said she was a nurse. She came over and started doing CPR.

"From that moment everyone was just gathered around. There was a lot of panic and chaos."

Mr Walizada said a woman, believed to be the mother of at least one of the children, rushed over as crowds gathered around the resuscitation attempt.

"As soon as she came over she dropped on the floor. She collapsed, passed out," he said.

Laila Wali says she was shocked by what happened.(ABC News: Cason Ho)

Laila Wali, who also saw the incident unfold, said she had spotted the children before they fell in the water.

"Just really, really shocked [about] what happened … I realised the two children I saw before were walking near the water," she said.

"I just feel sorry now, why I didn't stop those two kids."