A fifth boy has been confirmed safe after a police chase in Perth ended in the deaths of two teenagers when a group of youths jumped into the Swan River to avoid being arrested.

Key points: Police have recovered the bodies of two boys from the Swan River at Maylands

Police have recovered the bodies of two boys from the Swan River at Maylands Two others were recovered from the river and a fifth has been confirmed safe

Two others were recovered from the river and a fifth has been confirmed safe The group of five teenagers was being chased by police before entering the river

Police said the body of one teenage boy had been recovered from the water on Monday night.

They issued an update on Tuesday morning confirming another teenager had been found dead.

"Tragically, Water Police have recently located a second body believed to be that of the second teenage boy who was unaccounted for after search efforts that commenced in Maylands yesterday (Monday) afternoon," a police spokesman said.

WA Police Commissioner Chris Dawson confirmed five teenagers were in the group being chased by police.

Sorry, this video has expired Second boy found drowned by WA police

In addition to the two boys who died, two members of the group had been recovered alive from the river, while police on Tuesday afternoon confirmed a fifth boy had been found and was safe with family members.

A search of the river around Maylands, involving specialist officers from the police Mounted Section, Water Police and Police Air Wing, along with SES volunteers, has now finished.

Police rescue one of the boys from the Swan River. ( Supplied )

Commissioner Dawson said police were unsure whether the fifth boy had entered the water along with the other youths.

Boys accused of 'jumping fences'

Officers had been called to Tranby Road about 3:15pm on Monday when it was reported youths were "jumping fences" in the suburb of Maylands.

The Commissioner said police were conducting "proactive patrols" when they were flagged down by a member of the community who alerted officers about the boys' activities.

Officers found and chased the boys, four of whom they saw run into the river.

Police divers were deployed to search the river for the missing boys. ( ABC News: James Carmody )

Commissioner Dawson said Tactical Response Group (TRG) officers who happened to be nearby joined them when they saw the events unfolding.

He said Water Police and the TRG "rib", an inflatable boat, were deployed.

Sorry, this video has expired Police search Swan River after teenagers enter water during chase

Commissioner Dawson said two boys were recovered closer to either bank, but another two got into difficulties in the middle of the river and went underwater.

He said "several" officers went into the river, but was not sure exactly how many.

Police officers on horseback took part in the search of the Swan River and surrounding areas. ( ABC News: James Carmody )

Incident treated as a death in custody

The Commissioner declined to comment on reports of a house being ransacked nearby.

"I think any matters concerning offending need to be put squarely to one side," Commissioner Dawson said.

Commissioner Dawson said the families of the deceased boys had requested he not release any particulars about them, something he would respect.

SES crews marked search locations along the river as part of the search. ( ABC News: James Carmody )

Their deaths would be treated as deaths in police presence, which are treated the same as a death in police custody, and the state's coroner will prepare a report on the incident.

Community overcome with grief

Aboriginal Legal Services WA chief executive Dennis Eggington said the incident had left a whole community in mourning.

"I was terribly saddened and horrified because anyone who knows our community will note that the vast majority of the Noongar community today will be in mourning," he said.

"My heart goes out to the families who are obviously trying to come to terms with what's happened.

Dennis Eggington says there is a huge level of grief within the local Aboriginal community over the Swan River deaths. ( ABC News: David Weber )

"I haven't seen this level of grief, bordering on anger, but certainly grief and pain for a long, long time.

"The Police Commissioner said it happened within police presence. It's a distinction, but the same outcome — it's a death in custody and needs to be treated as one.

"I'm urging the State Government, because of the seriousness of the matter, to put extra resources into this inquiry and into the coronial inquest and give the answers to the families. They deserve that, they're suffering enough."

Mr Eggington said people were rallying together to provide support to the families, particularly the young boys who survived the incident, who were getting support from various agencies.

"The young boys would be absolutely in terror, running frightened and hitting the river, and being in more trouble and being more frightened, and I couldn't think of anything worse than the scenario where they've drowned in the river," he said.

"It's a terrible tragedy for the families, but for those young boys, scarred for the rest of their lives being a part of a horrible situation like yesterday (Monday), hopefully they get the support they need."

The federally funded National Indigenous Critical Response Service is supporting the grieving family members.

The organisation's national coordinator Gerry Georgatos described the boys' deaths as a "harrowing, staggering tragedy".

"The families are highly distressed, they're grieving as any family would at this time," he said.

"In terms of police and what led to the children running into the river, no one will know until the inquest.

"At the moment (the families) are consumed, soaked up in the tragedy, in the loss of young ones far too young."