Florida ? A support frame collapsed at a high-rise construction project Saturday, killing three workers who became trapped in quick-drying concrete as co-workers dug to try to free them, authorities said.

The workers were on the 27th level of the building when the frame structure below them gave way, dropping them to the 26th floor, said Capt. Al Cruz, of Miami-Dade Fire Rescue.

A 3-foot layer of hardening concrete completely encased one worker and partially buried the others, fire rescue officials said. The cause of the frame collapse was not immediately determined.

The identities of the three workers killed were not immediately known. A fourth worker was taken to a hospital with suspected heart trouble, authorities said.