Queensland Police said a 69-year-old Brisbane man was the pilot of the light airplane which came down near Scarborough at about 9am on Sunday after taking off from nearby Redcliffe Aerodome where his family were waiting.
Another man and two children "younger than teenagers" were the other passengers killed but their identities have not yet been confirmed.
Inspector Craig White said the pilot's family at the aerodrome became aware of the crash after they began looking at social media when the single engine, four seater plane failed to return.
"There are a number of family of the pilot who were at the Redcliffe Aerodrome at the time of the accident," he said.
"I understand it was a bit of a family day ... a family joy ride.
"The family became aware when they knew the aircraft hadn't returned on site, also they began looking at social media posts."
Media reports suggest the plane - a Rockwell Commander 114 light airplane - may have flipped after engine trouble prompted the pilot to attempt to return to the landing strip.
"This is a tragic accident. It's leading up to Christmas and this is the last thing that any family needs to go through at this time of year, or any time," Insp White said.
"The (pilot's) family are deeply traumatised as you would expect."
A multi-agency operation is underway with water police and divers along with the force's forensic crash unit assisting other agencies including the Australian Transport Safety Bureau.
ATSB Chief Commissioner Angus Mitchell said early reports are that the plane crashed not long after takeoff.
He said a Brisbane ATSB team were currently on site to help recover the plane from "quite inaccessible" mangroves off Scarborough with Canberra investigators set to arrive on Monday.
He said a preliminary report on the crash's cause would be available in six to eight weeks.
Anyone who witnessed the crash or with information have been asked to contact police or the ATSB.
6°C