Firefighters battle a blaze at the CTV Ottawa newsroom Nepean on Sunday. (CBC)

An overnight fire has destroyed the CTV newsroom in Ottawa and reportedly caused at least $2.5 million in damage.

The fire started sometime before 4:30 a.m. ET Sunday at the building. It tore through the newsroom for CTV Ottawa, formerly known as CJOH-TV, on the second-floor of the building in the southern suburb of Nepean.

A security guard was on duty when the flames broke out at the building at 1500 Merivale Road.

He suffered no injuries and by mid Sunday morning it appeared that nobody else had been injured.

It took 70 firefighters and 18 fire trucks more than two hours to bring the fire under control, CTV.ca reported. The entire newsroom, home to television cameras, editing equipment, computers, and archival footage, was completely gutted, officials said.

Among the items destroyed is 37 years' worth of archival videotape of anchor Max Keeping who is retiring this spring.

"We're very fortunate that nobody got hurt but we've lost a great deal," Keeping told CBC News on Sunday.

"And I guess on top of that is the fact that this building [is] historic in Canadian broadcasting. You know, [in] 1961 when it was opened, it was the CTV national news that operated out of here in those first years, and so many major productions came out of here and a lot of that may have been lost."

The cause of the fire has not immediately been determined.

Newscast to air Sunday

It could be days before staff are able to return to the facility, CTV.ca reported, however management officials are planning to continue operations at the A Channel newsroom in Byward market.

"We're already ready to continue our broadcast today and we'll be on the air later this afternoon," Keeping said.

"It's a very sad day as you can see. I just found out a couple of minutes ago because my daughter works just down the road and she phoned me up and said the place where I've worked for the 30 years was on fire. So it's very upsetting right now," said Claude Davis, who works at the front desk of the newsroom.

"I don't know how bad the damage is. I just got here and it's very traumatic right now," Davis told CBC News.

Merivale Road between Clyde Avenue and Baseline Road was closed to traffic until early afternoon on Sunday while authorities investigated. The stretch of roadway re-opened at around 1:30 p.m.