Two men and two children have died after a light plane crashed into mangroves off the Queensland coast on Sunday morning.

An investigation is under way into why the four-seater aircraft crashed shortly after taking off from Redcliffe airfield, north east of Brisbane, about 9am.

Four bodies, including that of the 69-year-old male pilot, were recovered from the aircraft at about 12pm.

Another man and two children not yet in their teens also died in the crash. Police were yet to confirm their identity, but do not believe they were related to the pilot.

Queensland Police Inspector Craig White said members of the pilot’s family were at the Redcliffe aerodrome at the time of the crash.

“I understand it was a bit of a family day,” he told media on Sunday. “The family are deeply traumatised as you’d expect.”

White said the families became aware of what had happened once the aircraft did not return and they saw posts on social media.

“This is a tragic accident,” he said. “It’s the lead up to Christmas and this is the last thing that any family need to go through at this time of the year, at any time.”

Two children among four dead in light plane crash off Queensland coast

The flight was a “joy flight” and appeared to have been prearranged, he said.

The plane could be seen floating upside down in the wake of the crash as water police and forensic divers worked at the scene.

Australian Transport Safety Bureau chief commissioner Angus Mitchell said a “very experienced team” was working to understand what caused the crash.

Early reports suggested the plane went down shortly after takeoff but air traffic control was yet to confirm its movements, he told reporters.

“We will of course get any evidence we can from the actual plane itself but equally from other sources such as air traffic control and witnesses,” he said.

He called for any witnesses or people with relevant information to contact Queensland Police or the ATSB.

Mitchell said the ATSB was working to recover the wreckage but the tide had gone out, making it difficult to get a barge in.

“My understanding at the moment is it’s really ankle deep water … because the tide is going out,” he said.

“It was slightly deeper at the time of the accident.”

Earlier on Sunday, Queensland police commissioner Katarina Carroll said police and divers were confronted with a difficult situation.“The plane is in a very, very difficult situation, difficult position in the wetland area, and we have currently got police and divers travelling to that area, and that’s all I can say at this stage.”