The pepper spraying of Syrian refugees in Vancouver has prompted sweeping condemnation, with Prime Minister Justin Trudeau saying it doesn't represent Canada's attitude toward migrants.

Vancouver Police are investigating the Friday night incident as a hate crime. Police said a large group was gathered outside a Muslim Association of Canada Centre during a "welcome night" for newly arrived Syrian refugees when a man on a bicycle sprayed the crowd.

About 15 people, including children, were treated for exposure to the spray, police said.

"This isn't who we are -- and doesn't reflect the warm welcome Canadians have offered," Trudeau posted to Twitter on Saturday.

Nawal Addo said she was standing outside with the refugees, who were waiting for a bus back to their hotel, when suddenly everyone began to cough and feel their eyes burning.

"We saw people coming out from the building and they were in worse condition than us," she said. "Their eyes were really puffed up. They weren't able to open their eyes."

She said it appeared the fumes had gotten inside the entrance, where it affected people more powerfully inside the enclosed space. Some were vomiting and one victim was a two-year-old girl, Addo said.

She said she didn't see the man on the bicycle.

"There was only one witness and he didn't even see his face," she said.

She said the welcome night was the first social event in Canada for many of the newly arrived refugees. They had a "very nice" evening getting to know one another over dinner, she said.

Addo, a 16-year-old of Syrian background who grew up in Canada, said she doesn't want to assume the worst.

"I hope it wasn't a hate crime. You never know, maybe it was just a nut case that was going around. But if it was, then I'll just say that Canadians should know better."

Vancouver Police Chief Const. Adam Palmer said a number of sections within the department were assisting with the investigation, including a hate crimes detective and a Muslim liaison officer.

He said the suspect on the bicycle was wearing a white or grey hooded sweatshirt and had a slim build. Police are canvassing the area for video and physical evidence and interviewing witnesses and victims. Police made no arrest on Saturday.

"It's a very troubling situation, and the actions of one man have shed a negative light on a lot of the positive work that's been done to welcome the Syrian refugees into our communities," Palmer said.

"We're going to put the necessary resources into this investigation, to identify the suspect, solve the crime, and make sure we assist the victims in this troubling incident."

The Muslim Association of Canada issued a statement saying the incident was "regrettable" and urging law enforcement to take swift action against the perpetrator.

"However, it is important to note that this incident is dwarfed by the level of generosity and welcome from Canadians across the country. Canadians of all walks, up to Prime Minister Justin Trudeau, have welcomed refugees and chosen tolerance," it said.

"As Canadians, we will continue to draw on our shared values to reject this violence and send a clear message to individuals and groups that seek to divide us."

B.C. Premier Christy Clark, Vancouver Mayor Gregor Robertson and federal Immigration Minister John McCallum also expressed outrage at the alleged attack.

"Last night's attack on refugees is intolerable, regardless of motivation," Clark tweeted. "Please join me in condemning it, and welcoming new Canadians."

McCallum said he was appalled.

"Canadians know that this incident is an affront to our values as a nation, and is at odds with the overwhelmingly positive welcome that Syrian refugees have received in communities across our country," he said in a statement.

"I would also like to assure recently arrived Syrian refugees that those who gathered last night to support and welcome them embody the Canadian spirit. This attack in no way represents their new home."

The government has committed to welcoming 25,000 Syrian refugees to Canada by the end of next month. Thousands have already arrived.