Two men have been crushed to death after a concrete slab fell at a construction site at Brisbane's Eagle Farm Racecourse.

The workers, aged in their 20s, were killed when the slab came loose from a crane about 4pm on Thursday.

Other workers rushed to help but were unable to save them.

Queensland Ambulance Service supervisor Glen Morrison said the men were killed by a large slab being moved by a crane.

“As a result of one of the slabs being moved, it’s crushed the two gentleman who were down in a hole at the time,” he told reporters at the scene.

Workers removed the slab before ambulance crews arrived.

An ambulance officer was then sent down to see if any help could be rendered but it was too late.

“Unfortunately they were both deceased at that time – so very unfortunate and very distressing for the officers concerned,” Mr Morrison said.

The men had been working on a multi-million dollar redevelopment at the track, which includes the construction of hundreds of new stables.

Queensland Racing Minsiter Grace Grace said she was saddened by the deaths.

“My heart goes out to the family and friends of those who have tragically lost their lives,” she said in a statement.

“I want to express my deepest sympathies to everyone concerned.”

Ms Grace said Workplace Health and Safety Queensland had begun a “thorough investigation” and she expected to receive a report into the incident “as soon as possible”.