Toronto's Yorkdale Shopping Centre was locked down after gunfire rang out at the popular north-end mall Thursday afternoon.

Police received "a number of 911 calls" shortly before 3 p.m. ET Thursday reporting a shooting, Supt. Rob Johnson told reporters at the scene Thursday evening.

Investigators have determined that an altercation broke out between two groups of men in the southeast corner of the mall, he said. At one point, one of the men pulled out a gun and fired at least two shots.

The men fled the scene, he said. Earlier, police tweeted that they were seeking two men in their 20s, one of whom may be carrying a handgun.

Mall closed for the day

"We are in the process of interviewing witnesses and looking for evidence," Johnson said.

No one was injured as a result of the gunfire, he said. However, two people were treated for minor injuries trying to flee, he said.

Earlier, paramedics said they transported one person to hospital for a medical issue unrelated to gunfire.

The mall tweeted that it would be closed until Friday morning.

"Yorkdale is secure and we are co-operating with police to safely evacuate the centre," the mall said. "We expect to open as scheduled tomorrow morning at 10 a.m."

Johnson said officers helped employees get back into the mall to retrieve their belongings, and help managers lock up their stores for the night.

Police are helping patrons leave the mall and are not letting anyone in. The mall will be closed for the rest of the day. (Paul Borkwood/CBC)

CBC News videographer Mary Webster was in the mall when she heard a loud bang, followed by a second. Patrons huddled in the back of the Roots store while someone set off an emergency alarm.

"People were crying," Webster reported from the scene.

Mall staff asked patrons to file into a hallway and then escorted them out through an underground parking lot, she said. Some patrons left all of their belongings behind.

'Was just a lot of chaos'

Alexis Uiga and her daughter Samantha were having coffee together in the mall when they heard the shots.

"We thought it was a balloon or something popping, it just didn't register what it was," Uiga told CBC News.

Once they heard another shot they realized what was happening and hid under a ledge, she said.

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"I had a little girl who got separated from who she was here with and she was just clenched on to me and another woman and her son were falling over me," Alexis said about the scramble to take cover.

"It was just a lot of chaos then everything just went quiet and that was it."

Alexis said all that was going through her mind was to protect her daughter and the strangers around her.

"I can't describe it. I never thought I'd have been in the middle of a shooting," she said, adding all you can really do is "take cover, be quiet and just hope that you can get through it and get back home to your loved ones."

Alexis Uiga and daughter Samantha were having coffee in the mall when they heard gunshots. (Paul Borkwood/CBC )

Another mall patron, Connie Chen, said she was "really terrified" when she heard two shots.

"It was like a firecracker," she told CBC Toronto. "We saw people running and we started to run. The first sound was really loud."

Natasha Narine, an employee at the MAC cosmetic store, said the mall was "very crowded" because it's the last week before school "and everybody is back to school shopping."

Police have cordoned off the mall entrances and are evacuating the building. (Mary Webster/CBC)

In a statement, Mayor John Tory said "people should not have to worry about gun violence," no matter where they are in the city.

"There are too many guns available to criminals in the city and I am determined to end that with the help of our police and our government partners," he said. "I am relieved that there are no reports of injuries from gunfire and I hope that remains true."