A 15-year-old has died in hospital, days after he was crushed at a Brisbane gym while trying to bench press about 100 kilograms.

Ben Shaw was found by a staff member at the Pine Rivers PCYC gym on Tuesday evening pinned to a bench after the weightlifting accident occurred.

It was not clear how long he was trapped.

"Ben passed away yesterday afternoon with his family and friends around him," his family said in a statement.

"Ben was able to leave a legacy and donate his organs and tissue, giving life to others.

"We'd like to thank everyone who has been involved in Ben's care, including all friends and family."

Tributes for Ben began pouring in on social media from loved ones and friends.

"You were my best friend and you will be missed so much!" one friend wrote.

"I can't thank your parents enough for how they've raised you to be such a great mate, they would be so proud of you just as I am," another said.

Sharon Hickey, the president of the Pine Central Holy Spirit Hornets rugby league club, described Ben has a promising all-rounder.

"As a club we will be assisting to see the world through Ben's eyes and ensure his legacy lives on in support of his parent's and family," she said in a statement.

'Thorough investigation' will examine incident

Queensland Health Minister Cameron Dick described Ben's death as "a very sad and tragic event".

"I do know that Workplace Health and Safety Queensland are investigating the matter and they will conduct a thorough review of what occurred and will be very diligent in their investigation of this very sad event," he said.

"When that report is prepared it will be considered further by any prosecuting authority that's relevant to the matter, but one step at a time.

"We'll look very carefully at the incident and prepare a thorough report, keeping in mind always the very sad and tragic impact it's had on this young man's family."

The investigation will scrutinise CCTV footage to determine exactly what happened.

The Pine Rivers gym has been closed since the accident. ( Supplied: Facebook )

PCYC gym and fitness centre rules state that children under 16 years of age are not permitted to use weights equipment without proper supervision.

It also states members use the equipment at their own risk and management assumes no responsibility for any injury that may occur.

After the incident, PCYC chief executive Phil Schultz said the organisation would fully cooperate with the investigation.

"This is a terrible incident and everyone here at PCYC Qld has been impacted by it," he said.