A series of explosions rocked Toronto's financial district on Monday (1 May) afternoon, forcing police to close off a section during the evening rush hour.

Heavy smoke billowed out of the sewer grates, which the fire department said could be due to a power transformer explosion.

A Toronto police spokeswoman said that there were no injuries reported and that police and fire engines were at the scene.

Trains were bypassing the King St subway while traffic was being diverted from the area where the blast took place at the corner of King and Bay Street.

CBC News said that firefighters were able to contain the blaze which started at around 5.15pm, Fire crews will be entering the vault to douse any remaining hot spots, the Toronto Fire Services Platoon Chief Kevin Shaw said.

Matthew Pegg, the Fire Chief and General Manager of Toronto Fire Services said that Toronto Hydro had de-energised the vault and are pumping out rain water before assessment and repairs can start.

Toronto Hydro's spokesperson Tori Gass said that it still has not been ascertained what caused the explosion, saying that it was still to dangerous for its inspecters to enter the area.

"It's going to be quite messy down there, quite toxic. I would say we're not going to have answers quickly, unfortunately," Gass said.

In its latest tweet, Toronto Hydro said: "Crews are pumping water and drying equipment before being able to access and begin repairs in the vault."