A fire that tore through a townhouse on Lyon Street in Ottawa's downtown Monday morning appeared to have started on a balcony. (Rebecca Zandbergen/CBC)

A fire that started early in the morning at a three-floor condo building in Ottawa's downtown on Monday left several streets closed for the morning rush hour.

Firefighters were called to 327 Lyon St. just after 4 a.m. Monday.

About 70 firefighters responded with 12 trucks and five ladders to the fire that appeared to have started on one of the balconies.

Bonnie Cohen, a neighbour, said she at first mistook the sounds of the fire for something else.

About 70 firefighters responded to the apparent balcony fire with 12 trucks and five ladders. (Rebecca Zandbergen/CBC)

"We were sleeping and got woken up by what sounded like really, really loud rain, but it was crackling," she said.

"We smelled smoke and all of a sudden, we opened the blinds and there was fire on the balcony next door — or that's what we saw — and we threw on some pants and came outside."

Steve Bowman, another neighbour, said he watched the flames climb as high as the roof of the building.

"I just heard somebody screaming and I looked out on my balcony and all of a sudden, I heard smashing glass — everything going nuts over there," said Bowman.

"Flames, lots of flames, and lots of black smoke."

Police had closed Laurier Avenue at Lyon Street, Gloucester Street between Kent and Bay streets and Lyon Street at Nepean Street.

OC Transpo had also been advised of the road closures.