All of the facts have yet to emerge in a police shooting at a Toronto subway station, but the incident has renewed debate over how officers in Canada's largest city use force.

A few dozen of protesters turned out Sunday night for a rally outside the downtown subway station where an 18-year-old was shot Friday night and sent to hospital.

One of the protesters, Sakura Saunders, says frontline officers are too quick to shoot in confrontations and that only senior officers should have guns.

Ontario's police watchdog, the Special Investigation Unit, believes four of nine officers at the scene fired their weapons.

Media reports say witnesses saw a man on a subway train holding what appeared to be a gun before police arrived.

The SIU confirms it has recovered a weapon, but hasn't confirmed what type.

One transit rider, Jessica Wong, says she was on the train when police approached a man and told him to put his hands where they could see them, with the man yelling back "I don't have anything to live for anyways."

Wong said in an email officers had their guns pointed at the man when she and others started getting off the train, and that not long after she heard a number of shots.

"That is when everyone started running up the staircase and escalators. People who were coming down were going back up, people were even running up (the) down escalators," she wrote in an email.

The SIU, which is automatically called to investigate cases where someone is killed or suffers serious injury when police are involved, hasn't said whether the teenager is still in hospital but says he is expected to survive.

Saunders said in her view police went for their guns too quickly in the confrontation.

"It seems from the witness accounts that the police did not take time to assess the situation before firing an excessive amount of bullets," she said.

Police deal with threats that emerge, Chief says

Police Chief Bill Blair declined to comment on the subway shooting in a television interview Monday, but said that officers must have the option of using firearms even when dealing with the emotionally disturbed.

"When officers are confronted with someone with a gun, that's an incredibly dangerous situation, and frankly the circumstances there quite often require that less lethal options aren't appropriate," he told City.

"Police officers have to deal with the threat that they're confronted with. And so it's the behaviour of the individual, not necessarily the underlying emotional condition or mental health condition of the individual," he added.

"Someone with a weapon, particularly a firearm, represents an enormous threat to public safety and police officers have to respond to that. And it's very very unfortunate when that also involves a person who's suffering from an emotional disturbance or mental illness."

There has already been considerable debate over how Toronto police use lethal force.

In July there were noisy protests after 18-year-old Sammy Yatim was shot on an empty streetcar — an incident that was caught on video.

An officer faces a charge of second-degree murder in connection with the case, which is awaiting a hearing to be held next year to determine if there is enough evidence to send the case to trial.

Toronto police have also launched a review of use-of-force policies and an ongoing coroner's inquest is looking into the deaths of three Toronto-area residents who were gunned down by police at different times over the past three years.