Four people in Côte Saint-Luc have tested positive for COVID-19, prompting the mayor to urge residents to self-isolate to prevent the spread of the virus.

Côte Saint-Luc Mayor Mitchell Brownstein told CBC News he is concerned his city could become the "epicentre" of the COVID-19 pandemic in Quebec.

Quebec's director of public health, Dr. Horacio Arruda, was more cautious in his assessment, urging municipal leaders to allow public health officials to assess what is happening before making such blanket statements.

"It's important to have not only the aspect of your own city, but what is going on around," said Arruda. "Sometimes things are moving really fast. There are rumours and stories mixed up with other ones."

Brownstein suggested that the province should consider putting Côte Saint-Luc in lockdown.

Regional public health director Dr. Mylène Drouin, whose territory includes the entire island of Montreal, says a decision to lock down a community would have to be based on a close look at the epidemiological data and an evaluation of how well the measures now in place are working.

"It is a provincial responsibility," she said. "I think at this time we cannot take those decisions without having a public health analysis."

She said it would be the responsibility of the province to impose specific measures on Montreal — a move that might be plausible, given the dense urban setting.

'Don't shake hands. Don't kiss'

All of Montreal's large synagogues are now closed, and public health authorities, as well as Brownstein and leaders of Jewish congregations have urged people not to gather for the dinner for Shabbat, the Jewish day of rest, which begins Friday at sundown.

Brownstein said three of the people infected recently attended the Congregation Beth Chabad community centre and synagogue.

The fourth person lives in the King David assisted living facility and attended a wedding at the Shaar Hashomayim synagogue on March 12. That person was transported to the Jewish General Hospital Tuesday.

Beth Chabad is asking all congregants who have been in the synagogue since March 14 to place themselves in self-isolation. The centre has been closed since Monday.

"I'm asking people not to shake hands, not to kiss. In our community, that's like a novelty," said Sarah Raskin, the co-director at Beth Chabad.

"Don't shake hands. Don't kiss. Just shake your head and say hello from far away."

Rabbi Adam Scheier of Shaar Hashomayim said his synagogue had been rented for the wedding which the infected person attended. He said public health officials have since gotten in touch with the synagogue to let them know.

"It's hard for us to wrap our heads around this, but the world has changed so drastically in the eight days since that wedding took place," he said.

"At the time of the wedding, and even into the next day, none of the synagogues in Montreal had closed."

Scheier says he urged his employees present at the wedding to self-isolate.

Three confirmed cases were traced back to the Beth Chabad community centre and synagogue. (Jay Turnbull/CBC)

'Our worst nightmare'

"We know we have a dense city, [we] live close together, many religious institutions as well as senior residents and hospitals," Brownstein said. "This was our worst nightmare."

Brownstein said the city had tried to shut down events, such as weddings, to avoid such a situation.

The city enacted state of emergency measures Tuesday, which would allow the city to call public health and Montreal police to shut down events of over 10 people.

All the synagogues in the city agreed to shut down as of yesterday, he said. Shaar Hashomayim, where the wedding took place, is located in neighbouring Westmount.

"It's a shame it took until now," he said.

He said the city is dealing with a "mushrooming" situation, because snowbirds — elderly residents who go down south during the winter months — recently returned from places such as Florida.

"We're trying to get this all to stop, but we don't know where the virus has spread to."

Brownstein said Quebec public health will investigate when and where the confirmed cases went and will have details for the public soon.