Fire crews in Ottawa have a major blaze in the city's historic ByWard Market area under control.

Flames were first reported around 11:30 a.m. ET on the roof of Vittoria Trattoria, a restaurant in a century-old building at 35 William St., before the fire spread to the buildings on either side.

The ByWard Market sits just east of such landmarks as the Château Laurier and Parliament Hill, and is a popular bar and restaurant district.

Fire on Williams street officially under control. Very proud of <a href="https://twitter.com/OttFire?ref_src=twsrc%5Etfw">@OttFire</a> firefighters who worked swiftly and diligently. <a href="https://t.co/bwC0IOzM7o">pic.twitter.com/bwC0IOzM7o</a> —@ChiefAyotte

By 11:50 a.m., firefighters were being called off the roof and out of the building due to "rapidly deteriorating conditions," according to fire department photographer Scott Stilborn.

The roof of the building later collapsed, fire chief Kim Ayotte said during an update near the scene around 2:30 p.m.

At its peak, the fire reached four alarms, involving about 40 fire trucks and as many as 150 firefighters.

Fire in Ottawa's historic ByWard Market 1:15

"We made good progress, and I don't think the fire's going to spread beyond where it is right now," Ayotte said.

There were no injuries, Ayotte confirmed.

He said the fire spread to neighbouring buildings along the roof line, causing significant damage to as many as four structures.

Late in the evening, the fire department said it estimated the damage at $2 million. It said owners on William Street would have to wait until Saturday to return to their businesses.

Ayotte said fire crews used a large volume of water to put a "quick stop" to the blaze.

"We wanted to save our heritage and the importance of this area, and, as a result of that, we put a lot of water in it."

While the city couldn't confirm precisely when 35 William St. was built, it said the building dates back to at least 1872.

Ayotte said it's too early to say whether the damaged buildings might be saved, or if they will have to be torn down.

The Ontario Fire Marshal will be involved in the investigation, Ayotte said.

Water pours from the Vittoria Trattoria restaurant and a neighbouring vape store on William Street. (Scott Stilborn/Ottawa Fire Services)

Ottawa Mayor Jim Watson said he appreciated the efforts of firefighters to contain the blaze and ensure no one was hurt.

He said he hopes people will come down this weekend to support the merchants.

"My message to residents is don't come down to gawk; come down to shop, and help these merchants during this difficult time," he said.

He said the market is an essential part of Ottawa.

"This is part of the heart and soul of our city. It's the oldest continuous farmers market in North America."

As businesses rebuild, he said he wants the city to help rather than hinder by putting up red tape or other barriers.

"We want to ensure these buildings are restored as quickly as possible."

With the cooperation of <a href="https://twitter.com/OttawaPolice?ref_src=twsrc%5Etfw">@OttawaPolice</a> <a href="https://twitter.com/OttFire?ref_src=twsrc%5Etfw">@OttFire</a> and <a href="https://twitter.com/ottawacity?ref_src=twsrc%5Etfw">@ottawacity</a> we are insisting that no one attempt to access their stores at 55 ByWard Market Square until after 10AM Saturday morning. Pls RT —@OttawaMarkets