Open this photo in gallery Chief Public Health Officer Theresa Tam listens to a question on a teleconference about COVID-19 during a news conference on Sunday March 15, 2020 in Ottawa. Ontario and Quebec each saw spikes in confirmed cases Sunday as Alberta announced it has several cases of community transmission, forcing the closing of schools and daycares indefinitely. Adrian Wyld/The Canadian Press

Top Canadian public-health officials stressed that the window is closing to limit the exponential spread of COVID-19 as they escalated warnings and broad closings and identified new cases of community spread.

Across the country, provinces and cities have announced varying measures – some more stringent than others – to combat the spread of the new coronavirus.

The federal government issued an advisory urging Canadians travelling overseas to come home as soon as possible, cautioning that “new restrictions may be imposed with little warning.”

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Ontario and Quebec each saw spikes in confirmed cases Sunday as Alberta announced it has several cases of community transmission, forcing the closing of schools and daycares indefinitely. Quebec ordered the closing of all public and private recreational establishments including bars, while Ontario banned jail visits and postponed trials.

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Canada’s Chief Medical Officer of Health Dr. Theresa Tam said “our window to flatten the [growth] curve of the epidemic is narrow.

“This is our chance right here, right now. We need to act now and act together.”

In Ottawa, Vera Etches, the city’s medical officer of health, sounded a loud alarm Sunday, saying “there could now be hundreds to even a thousand cases in the community” based on local testing and global patterns for the novel coronavirus. Dr. Etches urged Ottawa residents to avoid leaving home for nonessential reasons to try to break the chain of transmission.

The Canadian travel industry has already started to contract. WestJet Airlines said it is cutting international seat capacity by 60 per cent and domestic flights by 40 per cent. The airline also announced that a passenger on a flight from Vancouver to Kelowna March 10 tested positive. Via Rail announced it is cutting half its service through the Windsor-Quebec City corridor.

Until Dr. Etches’s projection for community spread, Canadian public-health officials have mainly stuck to reporting confirmed case counts based on tests mostly limited to returning travellers who show symptoms. Those numbers have grown slowly for weeks. The national tally reached 313 cases Sunday afternoon.

Ontario had 140 confirmed cases Sunday, up from 103 one day earlier in the biggest single-day increase seen yet in Canada. Quebec reported 35 cases, up from 24. Alberta confirmed 56 cases, up from 39 Saturday. British Columbia did not have updated numbers late Sunday afternoon. Nova Scotia reported its first three cases, while Manitoba and Saskatchewan also had additional cases.

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Seven of the new Alberta cases stem from a single gathering in Calgary. "We believe we have reached an inflection point of this pandemic,” said Dr. Deena Hinshaw, Alberta’s chief medical officer of health.

“Based on what we are seeing, now is the time for additional action. This underlines the fact that gatherings can accelerate the spread of the virus,” she said. Two of the cases were acquired by an unknown source.

Quebec Premier François Legault made one of the strictest moves yet, ordering all cultural and recreational public and private spaces, including bars, theatres, yoga studios, ski hills and gyms, to close. Stores remained open, along with restaurants to avoid putting extra pressure on packed grocery stories. Quebec had already closed schools, like Ontario, and banned large gatherings. Other provinces such as Manitoba, with seven cases, have recommended similar measures.

Mr. Legault said the rapid growth in cases “confirm the importance of trying to give ourselves every chance to slow down this contagion in coming days.”

Like Alberta Premier Jason Kenney, Mr. Legault has called on the federal government to increase airport screening and restrict arrivals to Canada. Mr. Kenney said he has asked federal officials how Alberta could help. Mr. Legault said he will send public-health officials to Montreal’s Trudeau International Airport to ensure travellers are at least told they need to isolate.

The government announced screening Friday but travellers have reported little evidence of it since, and the government struggled to explain why. Prime Minister Justin Trudeau said the screening is being put in place and he has not ruled out stricter measures. Tourism Minister Mélanie Joly told reporters new measures will be announced Monday but offered no details. “We understand people have anxiety, and these exceptional times require exceptional measures,” Ms. Joly said.

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Peggy Sweeney said that when she arrived at Toronto’s Pearson International Airport Saturday night, returning from Mexico, she observed few exceptional measures.

Instead, she saw “two sanitizer containers from the time we got off the plane to the time we got through customs, and both were empty.” She did not see any signage informing travellers of self-isolation or other precautions they should take, and said that she was given no such advice by the border agent with whom she interacted.

“He said where did you come from, we said Cancun, he said go,” Ms. Sweeney said.

Dr. Tam could not explain why coronavirus mitigation information was not being provided to all returning Canadians, as Ottawa promised on Friday. This is a “rapidly evolving situation,” Dr. Tam said. “Right now, you might not see that message as yet.” ​

Ontario’s new measures announced on the weekend included suspending visits for inmates. The federal system also cancelled visits. The Ontario Court of Justice suspended all trials for the next 10 weeks except where the accused is currently in custody, in which case trials, bail hearings and urgent motions may go ahead.

Prabmeet Sarkaria, Ontario’s associate minister of small business, said the province is not currently considering a lockdown to respond to COVID-19 concerns, even as a top health official urged the province to close nonessential services. He instead asked Ontarians to “exercise a high degree of caution.”

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Dr. Kevin Smith, president and CEO of University Health Network in Toronto, told The Globe he hopes Ontario becomes more aggressive in social-isolation policies, including shuttering nonessential businesses.

“There’s no reason to think that we’re not going to look like Europe, so I believe to be prudent that is what we should be aiming towards,” he said. “I know there will be some who say that’s an overreaction. I would dramatically prefer overreacting to underreacting.”

With reports from Laura Stone, Sean Fine and James Keller

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