Winnipeg police have arrested at 17-year-old girl after they were called to Portage Avenue and Main Street in the city's downtown, where a masked person was reported to be waving a gun at vehicles and her own head.

Police later said the gun was not a real firearm.

It happened at the city's best known intersection on Tuesday morning, in front of many bystanders. Some posted videos and photos on social media as it unfolded.

"This was a significant event for the city of Winnipeg and members of the public, as it unfolded in such a public place," deputy police chief Gord Perrier told reporters at a briefing Tuesday afternoon.

The sound of sirens filled the downtown intersection just before 10 a.m. CT after numerous people called 911.

Police say when officers arrived, the suspect took off her mask, put the gun to her head and dropped to the ground.

As the officers approached her, she then got to her feet and started walking away with the gun in her hand. One of the officers tackled her and she was arrested without further incident, according to police.

No injuries were reported. Police say the incident was over within four minutes.

Perrier said officers at the scene were faced with an "extremely volatile" situation in such a busy intersection. He added that some videos he saw on social media made it appear as though the suspect had fired the gun.

"A lot of people were concerned — did she shoot herself or did that occur? And, you know, the first time I saw it, it was my exact same concern," he said.

'Not a real firearm,' says deputy chief

At the time, officers did not know if the suspect's firearm was real or not, said Perrier, who added that it was well after the arrest that they determined it was a replica.

"It's not a real firearm. However, it was presented as one," he said.

Perrier would not specify if was a toy, a pellet or airsoft gun, or another type of replica.

The teen has been charged with possessing a weapon for a dangerous purpose, causing a disturbance and public mischief.

Perrier declined to speculate on motives behind the incident. He said it's unclear if the suspect was trying to harm herself.

"That's one of the questions that's difficult to answer. Two reasons: one, that may have a personal health information overlay, and this individual is under the age of 18," he said.

"I can say [in] similar cases, such as this, that is one of the primary things that we're looking at and one of those things that we'll be leaning towards, both from an investigative standpoint and from a care standpoint."

He added that a mental health evaluation is generally standard in cases such as this.

Perrier could not say why the suspect was holding a rose and a piece of paper in her other hand.

'She kind of looked at me,' says witness

Among those who witnessed the incident was Jesse James Lane, who said he made eye contact with her as she stood about three metres away from his work truck.

Lane said he started recording video as he got out of his truck and asked her to put the gun down.

"She kind of looked at me, and we kind of made eye contact when she was waving the gun around a little bit," he said.

"I was like, 'You know, you should drop your gun. What are you doing?' And she … kept walking around, holding it to her head, and she did seem kind of distraught."

A woman was arrested at the corner of Portage Avenue and Main Street in Winnipeg on Tuesday morning after she walked into traffic, waved a gun around at vehicles, then put it to her head. 0:36

Cameron Murphy, who was driving a school bus through the intersection, saw her standing on the road with a white face mask on "like you'd see at the opera."

"She had what appeared to be a handgun, waving it around, pointing it [at] me [and] other people and then put it to her head," he said, adding the suspect had a letter or a piece of paper in her other hand.

I was nervous because of the unknown of what could happen. - Jason Krueger

He called his company's dispatchers, who then called police.

Jason Krueger said he became nervous when he saw her hold the gun to her head.

"I turned down Portage and got out of there," he said. "I was nervous because of the unknown of what could happen."

Lane said he took shelter behind his truck after armed officers with the Winnipeg Police Service's tactical unit arrived at the scene.

"I must say that the tac unit did a very good job of controlling the whole scene in general," he said.

"Just the way they handled it was very good because it's kind of a confusing situation when someone has a gun to their head."