Toronto police said emergency crews were called to District 45 on Finch Avenue West after 2 a.m. on Monday, reports Global News Canada.
"We received several phone calls from patrons inside (the nightclub) for the sound of gunshots," Duty Inspector Stacy Davis told reporters on Monday morning.
Davis said that there were reports of an altercation inside the club, but there were no information on the suspect yet.
Police chief Mark Saunders said the shooting was "very solvable" based on the high number of witnesses present, encouraging attendees to come forward.
"I find it disturbing when you've got over 100 people and someone would be brazen enough to pull out a gun and start shooting," he said.
The owner of the nightclub, said he and around 250 people were at the establishment at the time of the shooting, Global News Canada reported.
"I'm angry. I'm not happy about it. We planned for the night. We had over 40 security guards," he said.
On Monday, Toronto Mayor John Tory called the recent rash of gun violence "absolutely unacceptable", Xinhua news agency reported.
"I know Toronto Police are working non-stop to find those responsible for these shootings and to bring them to justice," he said, adding "I urge anyone with information that could help investigators solve these shootings to call police or Crime Stoppers."
The Mayor also repeated his calls for a handgun ban. Toronto City Council debated a handgun ban in June and more debates are expected to come.
The Toronto incident comes after two mass shootings in the US states of Ohio and Texas over the weekend claimed the lives of 31 people in total.
( With inputs from IANS )