It could take BC Hydro officials at least another day to figure out what caused a fire that burned through 14 circuit cables Monday, knocking out power supply to 20,000 customers in a large section of Vancouver's downtown core.

The force of the explosion blew out a manhole cover near West Pender Street and Richards Street, sending thick clouds of smoke into the air.

"All I heard was a big pop, and we came out and found out there's a fire underneath a manhole,'' said one observer.

Underground, a blistering fire that melted 14 circuit cables at one of the downtown core's major substations, left 20,000 customers without power. Major affected businesses include the Vancouver Sun newspaper and the BC Hydro offiices on Dunsmuir Street.

A hotel located near the manhole cover had to be evacuated because of concerns over the potentially toxic smoke.

The affected area stretched from Hastings Street on the north to Robson Street on the south and from Burrard Street on the west all the way to Cambie Street on the east. The Yaletown district was also affected.

The outage caused a mess on the roads and major delays with public transit. The Waterfront Station building had to be evacuated, but Seabus and SkyTrain commuters were allowed in. Bus services were also way behind schedule.

Without any electricity and no word on when it would come back, dozens of downtown businesses were forced to shut down for the day.

The power outage affected numerous traffic lights, disrupting traffic flow and making it difficult for passengers to cross downtown streets.

Vancouver police dispatched a dozen officers to help direct traffic at key intersections. But some people questioned whether that was enough.

Meanwhile, there is no official word on what caused the fire or how long any repairs will take to complete.

"It could be a short term fix and it could be several days. It's really hard to speculate until we get in and have a look,'' said a BC Hydro spokesperson.

With reports by CTV British Columbia's Jina You and Reshmi Nair