The men, aged 34 and 55, were working inside a pit when a concrete slab being moved by a crane fell onto them, crushing them to death.

The police Forensic Crash Unit was helping the investigation, with officers on scene on Friday morning.

Seven ambulance crews and four fire trucks rushed to the Lancaster Road, Ascot racecourse just before 4pm Thursday.

Workers on the site were able to remove the concrete slab, which is believed to have weighed up to 10 tonne, from the men but when paramedics arrived they were already dead.

"We sent one of our staff down into where the two workers were to see if we could render any aid but unfortunately they were both unable to be revived," Queensland Ambulance Service's Glen Morrison said.

The men were building part of the new stables that are being constructed in the centre of the track, part of at $37 million redevelopment of the Eagle Farm Racecourse.

The facility is the first of its kind in the world and will provide 400 stables as well as training and husbandry facilities.

A spokesman for Workplace Health and Safety confirmed and investigation is underway into how the incident occurred.

A number of other workers at the scene were treated for shock, but none required transport to hospital.

Witnesses were expected to be offered counselling on-site on Friday morning.

Representatives from Brisbane Racing Club failed to return Fairfax Media's call.

Racing minister Grace Grace expressed her sympathy for the friends and families of the two men who were killed and said she expected a full report into the incident to be provided to her.

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

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

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