"2 ppl killed in gunfire that broke out during party," police said in a Twitter message. "Deceased are a male and a female," said a second message by Police Chief Bill Blair.

He described the incident as "the worst incident of gun violence" in the city's history. "A lot of innocent people were injured tonight."

Blair told reporters that during a "very large party" with more than 200 guests "an altercation broke out between individuals" that lead to an exchange of gunfire. The shooting occurred on Danzig Avenue, near Morningside Avenue and Lawrence Avenue East in the city's east side after a fight at a crowded barbecue.

Blair said a 20-year-old man and a young teenage girl were killed, and as many as 19 were injured in the melee.

Constable Wendy Drummond added "not all of those victims are gunshot victims."

"We have a child, an infant, that is also a victim," she said.

The child was shot, said Blair, adding that the "infant will be fine."

Broadcaster CityNews reported that a 20-year-old woman was shot in the back and at least eight others aged 18 to 25 were taken to hospitals in the Scarborough area with gunshot wounds.

In another message, police asked, "Witnesses/people at party or nearby, please let us know what you saw/heard."

One "person of interest" is in custody, said Blair, as a swarm of police searched the area for possibly two or more shooters.