TORONTO -- Toronto's top doctor says now is not the time to prepare to ease pandemic restrictions in the city, even as the province starts rolling back restrictions in regions with lower case numbers.

Dr. Eileen De Villa said Monday that the concerning presence of new, more infectious variants of COVID-19 signals a transition to a "new pandemic."

"I understand the value of preparing for the time we can lift restrictions. From a public health perspective in Toronto, that time is not now," De Villa said.

Cases of a variant that first emerged in the U.K. have been linked to outbreaks in Toronto, and early screening has detected likely cases of variants that were first detected in South Africa and Brazil.

The three strains are believed to be more infectious and may cause more severe illness.

De Villa said what's known about variants so far is "alarming," and infections will likely rise more quickly if they become the dominant strains of COVID-19 in the city.

Her comments came as the Ontario government announced that a stay-at-home order for Toronto and two neighbouring hot spots would lift on Feb. 22.

The province is letting a state of emergency expire as scheduled on Tuesday and will gradually transition regions back to its colour-coded restrictions system.

Toronto, Peel Region and York Region will be the last to be moved to the system this month, although the province has said an increase in cases could change that plan.

De Villa stressed the importance of a cautious approach on Monday.

She noted that cases rose after the Thanksgiving and Christmas holidays -- when people likely had more contact with one another -- and said interactions between residents were set to increase when students in the city return to in-class learning next week.

"We will face a real challenge when presented with the opportunity to move about again with reduced restrictions but without more protection from COVID-19," she said.

The B.1.1.7 variant that originated in the U.K. has been linked to a worsening wave of infections across Europe.

Public Health Ontario had confirmed 219 cases of that variant as on Monday, with local officials saying the number is likely higher.

De Villa said the city can anticipate that COVID-19 cases will rise as they have in other jurisdictions with the new variants, "particularly if public health measures are not either maintained, and in some cases strengthened."

Toronto Mayor John Tory said Monday that the province's plan gives the city time to assess the variants' prevalence, and noted that Premier Doug Ford has been responsive to the city's concerns in the past.

"I'm confident that if things are not where they should be as we arrive at any particular date going forward, that the premier, as he has, will take that into account and do what is best for public health," Tory said.

Thomas Tenkate, a professor of occupational and public health at Toronto's Ryerson University, said the province's reopening plan seems to heavily rely on current case numbers rather than considering the new variants.

"These (measures) don't seem to be really taking that into account too much," he said by phone Monday.

He said keeping strict lockdown measures in place longer would likely be more effective, especially with the variants that can spread quickly.

He also pointed to the challenges of reopening different parts of the Greater Toronto Area at different times, as it might encourage people to travel to other nearby regions for services.

"Once you do that, you can really sort of provide people an incentive to sort of move," he said. "That's not helpful in regard to trying to control the spread."

This report by The Canadian Press was first published Feb. 8, 2021.