A plane that crashed into Perth's Swan River on Australia Day killing a man and a woman remains in the water.
The pilot and passenger died when the Grumman G-73 "Mallard" flying boat broke up on impact after 5pm on Thursday in front of horrified families.
"The plane seemed to be banking and then it looked like it was turning too sharply and just seemed to fall into the water," witness Mark Annette Stuart told AAP.
It's believed it was part of an airshow over the river ahead of Perth's annual Skyworks fireworks display.
The plane remained in situ overnight guarded by water police but could be removed on Friday pending a decision by the WA Department of Transport and the Australian Transport Safety Bureau.
The tragedy was captured on video and posted to social media by witnesses.
A huge plume of water could be seen as the plane hit the surface nose first.
Up to 10 pleasure craft on the river sped to the scene near Heirisson Island and tried in vain to rescue the occupants.
"His wings were pointing to the sky and to the water and we thought 'this is not good' then we saw it break into two pieces," witness Craig Newill told The West Australian.
Other witness reported a loud bang as the plane entered the water.
WA Police acting commissioner Stephen Brown said the cause of the crash was "unknown".
"For reasons yet unknown, it's entered the waterway, thankfully without injuring anyone else on the ground or any other people who are here at the event," he told reporters.
The fireworks were cancelled out of respect for the dead and to "conserve the integrity of the site", Perth Lord Mayor Lisa Scaffidi said.
More than 300,000 people had been expected to attend the Skyworks show around the river.
WA Police will provide an update on the incident on Friday.
