Toronto Police Chief Mark Saunders said it's "extremely disturbing" that crowds confronted police at Yonge-Dundas Square on Saturday, in some cases throwing objects at officers while cheering and recording what happened.

"It seems clear that for many there, it was a party atmosphere," said Saunders at a news conference Wednesday. "There were smiles, laugher, encouragement, booing and cheering — attitudes completely at odds with the threat in the Square."

Saunders was speaking about incidents that happened in the Square on Saturday and early Sunday, with many revellers out to take in Nuit Blanche, the all-night outdoor arts festival.

Late Saturday crowds of young people, many who appeared to be intoxicated, gathered in the Square.

Saunders said police moved in to the crowd to investigate reports of someone with a gun. When officers arrived, a fight broke out.

"During the course of that fight, many people fled and trampled a young woman," said Saunders.

Saunders said officers arrested someone carrying an imitation gun, a knife and a type of collapsible baton.

"At that point, the mood of the crowd changed," said Saunders, who described the crowd's behaviour at that point as "aggressive and threatening" despite the presence of young children.

Toronto Police Association president Mike McCormack said the officers at Yonge-Dundas square that night were concerned about their safety.

"They felt outnumbered, they felt surrounded and they were trying to again deal with a very serious call — a person with a gun."

"They are very concerned and they are very angry about it and rightfully so," he said.

Bottle thrown at police officers

Saunders said objects, including a bottle, were thrown at police during a confrontation that was captured on YouTube and played for members of the media at Wednesday's news conference.

Another video taken that night shows an officer being struck in the head by a thrown object, possibly a bottle.

Saunders said the objects cracked two police helmets while one officer suffered a broken hand bone.

He praised the "professionalism and restraint" of police at the scene.

"We're very lucky there were no serious injuries here," he said.

Saunders said the incidents show that a "wide-ranging discussion" about how to behave in public needs to happen to counter the perception that police confrontations are "to be encouraged, supported and broadcast."

Saunders said the crowd behaviour seen Saturday is "out of step" with Toronto. He also said police "will be ready" to handle any large crowds or incidents stemming from the Blue Jays appearance in the playoffs. The Jays first game is tomorrow afternoon.