The Saskatoon fire department responded to reports of explosions underground at the old Bay building just before 2:30 this afternoon.

"You could feel an impact on the ground … I looked out the window and there was smoke coming out next to the Cameco building on Second Avenue," said Doug Turnbull, who was nearby.

He said he felt numerous blasts.

"It went on for I would say two minutes. I would say 50 or 60 explosions."

It's causing power outages all over the downtown core, forcing many buildings to be evacuated including Midtown Plaza and the underground parking lots.

According to Saskatoon fire department an electrical vault had failed causing about seven feet of water to accumulate. This led to storm drain in the immediate area to also collapse.

City crews were called to pump water out of the vault, once this has completed a firefighter and city electrical personnel will entire the underground vault to investigate further.

They will attempt to fix the power supple and re-energise the system brining power back to the affected area on Second Avenue.

The technical rescue team is serving as safety backup.

An official said that the explosions people heard earlier could be from electricity arching underground.

Traffic is being rerouted around the area.

No injuries were reported.

A video showing black smoke from the explosions has been posted to the web.

ckomnews@rawlco.com