Two men in their mid-30s drowned at a beach north of Noosa on the Sunshine Coast on Saturday afternoon.
Bystanders pulled at least one man from the water at Teewah Beach after 3:00pm and began CPR while waiting for paramedics to arrive.
Neither man could be saved.
Three rescue helicopters and multiple emergency response vehicles were sent to the beach, which paramedics said was difficult to access.
A nine-year-old boy was airlifted to Sunshine Coast University Hospital in a stable condition.
A fourth person who swam out to try and rescue the swimmers was also treated at the scene but no longer requires assistance.
Queensland Ambulance Service spokesperson Michael Augustus said the beach was difficult to access.
"… We were also provided assistance from other people such as [National Park] rangers and Surf Life Saving Queensland so we were able to get people on the scene rather quickly," he said.
Surf Life Saving Queensland said the drownings had followed a day of serious incidents at the Sunshine Coast, and added that it was a "tragic reminder to only ever swim between the red and yellow flags".
"Our thoughts are with the loved ones of the two men today," SLSQ regional operations manager Aaron Purchase said in a statement.
"If you must swim at remote location, stay close to the beach and remain waist-deep.
"However, the safest place to swim remains at a patrolled location between the red and yellow flags."
