A construction platform collapsed Wednesday atop a high-rise condominium project, dropping two workers to their deaths and injuring a third man, authorities said.

The men were working on the 22nd floor of the downtown project, said Bennie Seth, a spokeswoman with the Jacksonville Fire-Rescue Department.

Two of the men plummeted to the ground. One was dead at the scene and the second died at a hospital, said Ken Jefferson, a spokesman with the Jacksonville Sheriff's Office.

The third worker fell four stories before being stopped by a safety device. He suffered minor injuries.

The cause of the collapse was not immediately determined, Seth said.

The building has been under construction for about a year and is scheduled to be completed later this year. According to the project's Web site, the condominiums will sell for $300,000 to $700,000 each.