BC Hydro crew members wait to go down the manhole at Georgia and Pender streets to investigate the explosion of an underground transformer that started a fire Monday morning. (CBC)

Power in the Vancouver downtown core will not be fully restored until at earliest some time Tuesday, following an explosion of an underground transformer that started a fire and sent plumes of smoke up through a manhole cover, BC Hydro said.

Crews were unable to enter the manhole during the day to assess the damage because the air inside was too hot, BC Hydro said Monday night.

Once the air had cooled down significantly in the manhole at Georgia and Pender streets, crew members were to go in for inspection and repair.

BC Hydro didn't know when power would be fully restored in the area, spokeswoman Susan Danard told CBC News.

"It's looking like a significant repair job will be required," she said. "It's turned out to be a larger problem than we had earlier learned of."

TransLink said public transit services were fully operational for the afternoon commute, although many buses had to take alternate routes out of Vancouver's downtown core. (CBC)

The power outage affected the east area of downtown bounded by Water Street, Cordova Street, Burrard Street, Nelson Street and Main Street, BC Hydro officials said.

An underground fire and explosion at 9 a.m. damaged 14 circuits at a BC Hydro substation, causing a power outage to about 20 per cent of downtown customers, Danard said.

The fire cut off power in a five-block radius and prompted the partial evacuation of a number of buildings Monday morning, Vancouver police Insp. John McKay said.

Police received reports of at least 10 incidents of people trapped in elevators.

Firefighters put out the fire shortly after noon.

Smoke not toxic: police

The smoke that billowed out of the underground access point was not toxic, McKay said.

"We are not concerned that there's any toxic gas at this point in time," he said. "The fire department indicated that it was just like standing next to a burning car. Obviously, you don't want to get your face in it or breathe it in."

Police advised people not to go to the downtown core because traffic was snarled all afternoon because traffic lights were out at some intersections, McKay said.

Vancouver police increased the number of officers to patrol downtown streets Monday night, he said.

"If the power is out still in the area, then we have the security issues of [there] being no lights in any of the businesses or the residences," he said.

Traffic lights were out throughout much of the downtown, and police were asking drivers to avoid the entire area.

But public transit services were to be fully operational for the afternoon commute, Drew Snider, a spokesman for TransLink said earlier in the day.

Snider said buses were finding it difficult to follow their normal routes through the downtown core, and many were being rerouted.