Police had received a call just before noon and that the incident happened at 34 Clayson Rd.
The worker fell into a hole, and a concrete slab fell on top of him, police said. There are unconfirmed reports that the hole was more than four metres deep.
The incident happened at a site managed by Rabcon Contractors Limited, according to a statement from the City of Toronto.
Rabcon was under contract with the city to install new sewer connections for an industrial building, the statement said.
Police confirmed early Tuesday afternoon that the worker had died. He was pronounced dead at the scene.
The Ministry of Labour is investigating the incident. The city said it was fully co-operating with the investigation.
"The City of Toronto offers its sincere condolences to the family and colleagues of this worker," it said in the statement.