Two men have been crushed to death by a concrete panel that collapsed at a construction site at Eagle Farm Racecourse in the northern Brisbane suburb of Ascot, the Queensland Ambulance Service (QAS) says.

QAS spokesman Glen Morrison said a concrete wall in a construction pit collapsed onto the men about 4:00pm.

"It looks like they were undertaking some large construction work involving some large cement slabs," he said.

"As a result of one of the slabs being moved, it's crushed the two gentlemen who were down in a hole at the time."

Mr Morrison said the slab was removed from on top of the men before paramedics arrived.

"We sent one of our staff down into where the two workers were to identify [them] and to see if we could render any aid.

"Unfortunately they were both deceased at that time - so very unfortunate and very distressing for the officers concerned."

The men were working on a multi-million-dollar development of infield stables. ( ABC News )

Industrial Relations and Racing Minister Grace Grace said she was saddened to hear of the tragic accident.

"My heart goes out to the family and friends of those who have tragically lost their lives," she said.

"I want to express my deepest sympathies to everyone concerned.

"Whilst the exact circumstances are unclear, Workplace Health and Safety Queensland is on site and a thorough investigation has commenced.

"I expect to receive a full report into this matter as soon as possible."

Paramedics speak to workers who witnessed accident

Mr Morrison said five to 10 other construction workers were in the vicinity when the accident occurred.

Paramedics have spoken to all of them and nobody has been transported to hospital.

The men were working on a $25 million development of 400 infield stables at the racetrack.

The project has been described by Brisbane Racing Club as the world's first major stable complex to be constructed infield.