Eyewitnesses describe the chaos and confusion that erupted when gunshots were fired in the national capital Wednesday.

Liberal MP John McKay told CTV News' Katie Simpson that when he first heard the gunfire, he didn't realize what was happening.

"Literally, I was just taking off my jacket to go into caucus. I hear this pop, pop, pop -- possibly 10 shots, I don't really know -- and thought it was dynamite or construction rather than something else," he said.

"Suddenly, security guards come rushing down the hallways, usher us all out to the back of the Parliament buildings."

McKay says it was only after he was off the parliamentary grounds and standing on Wellington St. that what had just happened sank in.

Karl Belanger, principal secretary to New Democratic Party Leader Thomas Mulcair, was also in the building when the shootings occurred.

"At first we just assumed it was construction noises, but then security came running by and told us to lock our doors. And by 'telling us,' I mean yelling at us to lock our doors and get back inside," he told CTV News Channel.

The Globe and Mail's Josh Wingrove, who recorded video on his phone of shots being fired near the parliamentary library, told CTV News that once the shooting began, it was "just chaos."

"It was a very quiet Wednesday morning, there weren't a lot of tourists, there weren't a lot of people in the building. And then we heard the breakout of gunfire," he said.

"It seemed like it came from the foyer, right from the main door, the front door that you would use to enter if you were an MP or a staffer or a press gallery journalist. In other words, there's no metal detector; it's just a door with some guards. So I don't know whether he came in there but certainly it seemed to set off there."