A shark killed a 16-year-old girl Saturday after she apparently jumped into a river in Western Australia to swim near a pod of dolphins, officials said.

The girl was bitten by an unknown species of shark during an outing with friends on the Swan River in the Perth suburb of North Fremantle,  state government and police officials said.

She was pulled from the water but died from her injuries at the scene after efforts to revive her failed, said Paul Robinson, acting police inspector for the Fremantle district.

"It's very early on, what we're being advised is that she was with friends on the river," he told a news conference.

"They were on jet skis. Possibly a pod of dolphins were being seen nearby and the young female jumped in to swim nearby the dolphins."

Describing it as a "very, very traumatic incident," Robinson said the family of the girl, who was from Perth, was "absolutely devastated by the news".

Experts had advised that it was unusual for sharks to be found in that part of the river, he said.

The state government warned people to take "additional caution" in the Swan River in North Fremantle and to abide by any beach closures.

It was the first fatal shark attack in the Swan River since a 13-year-old boy was killed in January 1923 in the Perth suburb of Claremont, according to reports at the time and a database run by Taronga Conservation Society.

The last fatal attack in any Australian river was recorded in 1960 when a bull shark measuring an estimated 3.3 metres (nearly 11 feet) killed a snorkeller at Roseville Bridge in Sydney, the shark incident database showed.

In February last year, a 35-year-old British diving instructor, Simon Nellist, was devoured off Sydney's Little Bay Beach, the first such attack in the city since 1963.

According to Sports Australia, 4.5 million Aussies swim regularly and at least 500,000 surf.