Two workers have serious injuries after they were struck by a piece of concrete in the city’s downtown core, police say.

It happened at a construction site near Bay and Walton streets, just south of Gerrard Street West, at around 1:30 p.m.

"There were three workers on the rooftop ... and were working with cement forms, during the process, they were preparing to move the forms when the forms collapsed," Sgt. Mark Hayward, a spokesperson for Toronto police told CP24 on site. "Two of the workers inside the forms, one of those workers sustained an injury, the other sustained the punctured lung. The worker on the outside sustained an injury to his back."

A 43-year-old man is being treated for a punctured lung, while another man, believed to be in his 40s, suffered back injuries, Hayward said. 

One victim has been rushed to a trauma centre and the other to a local hospital, according to investigators. 

Construction work on the multi-level apartment complex has been halted.

"The safety of all workers on site is paramount, and the area surrounding the incident has been secured," said Jennifer Nelson, a spokesperson for PCL, the construction company building the rental units. 

The Ministry of Labour is investigating the cause of the accident.