Const. George Tudos told Global News the incident happened after 11 p.m. He said paid duty police officers heard the sounds of gunshots.
Police said in a statement on Sunday that the officers found three male victims with serious, but non-life-threatening injuries at the front entrance of city hall.
Investigators said the three were taken to trauma centres in Toronto. A fourth male victim made his way to a local hospital.
Officers said all of those who were shot are from Ajax, Pickering and North York and between the ages of 16 and 30. They have since been released from hospital.
The incident happened after the Pickering Ribfest event closed for the night. The event takes place at the adjacent Esplanade Park, which is located northeast of Liverpool Road and Highway 401.
Police said they’re looking for a male suspect and that investigators “do not believe this was a random act.”
Pickering Mayor Dave Ryan said officials are “shocked and certainly disappointed with what happened.” He said Pickering is a safe city.
“This isn’t about Pickering. This isn’t what Pickering is,” he said.
“It’s frightening for a community to have these kinds of things happen.”
Ryan called for increased provincial and federal government support to address gun violence.
Meanwhile, anyone with information is asked to call police at 1-888-579-1520 ext. 2534 or Crime Stoppers anonymously at 1-800-222-8477.