Three teenaged suspects have been arrested after an attempted armoured car robbery during which a 37-year-old guard was injured overnight.

The incident occurred in the Avenue Road and Brookdale Avenue area, where witnesses reported hearing loud popping noises shortly after 1 a.m. Thursday.

"It sounded like a bunch of firecrackers," one witness told CP24's Cam Woolley.

Toronto Police Staff Insp. Mike Earl told reporters that the incident occurred at "approximately 1:11 in the morning," after a GardaWorld armoured car approached a TD Bank on Avenue Road to make a "typical drop."

"One of the guards exited the truck to enter the bank, at which point in time he was ambushed by three male suspects," Earl said at a news conference Thursday morning.

Police said the suspects opened fire on the guard, who then returned fire. The entire exchange lasted "approximately less than a minute."

Earl confirmed the guard had been shot several times, suffering life-threatening injuries. That guard was taken to Sunnybrook Hospital where he remains in critical condition. A second guard in the truck was not harmed.

The suspects were not able to get any money from the truck and immediately fled the scene on foot, police said.

Police said they later arrested three individuals in the Lawrence Heights area, and also seized a handgun they believe was used in the shooting.

"At this point in time we are not looking for any other suspects in this case," Earl told reporters.

"I can tell you now that these individuals are 18 years of age, and now facing charges of attempted murder, robbery-related charges with this incident, and conspiracy for a similar incident which happened on the 5th of June," Earl said.

On June 5, another armoured car was attacked in the Bathurst Street and Lawrence Avenue area, in what police are calling a "similar" attempt. Earl added that none of those arrested were known to police.

Jaden Beckford, Nicholas Cross, and Rashid Clarke face charges including armed robbery and attempted murder. All three are scheduled to appear in court June 19.

Anyone with information is asked to contact police at 416-808-7350, or Crime Stoppers anonymously at 416-222-8477 (TIPS), online at www.222tips.com.

With files from The Canadian Press