ONTARIO • Canada's largest province declared a state of emergency, forcing most retail stores to operate under new restrictions, and said it would change its vaccine strategy in its fight against a new and more dangerous wave of Covid-19.

Ontario, which is home to more than 14.7 million people, issued a stay-at-home order starting yesterday at 12.01am Toronto time.

Most categories of stores were required to shut, serving customers only through delivery or outdoor pickup. The order is in place for four weeks.

Even big-box retailers such as Walmart and Costco Wholesale, which were less affected by earlier restrictions from Premier Doug Ford's government, will now be limited to selling only essential goods such as food, cleaning products and pharmacy items.

The province reported 3,215 new virus cases on Wednesday and is marching closer to the peak level reached in January during the pandemic's second wave.

New variants have been rising rapidly and vaccines have been slow to arrive. About 15 per cent of the population has been given at least one dose, compared with 33 per cent in the United States, according to the Bloomberg Vaccine Tracker.

The number of Covid-19 patients in intensive care units rose 25 per cent between March 28 and Monday, the provincial government said.

The biggest problem spots are Toronto and Peel, a suburban region to its west - the two zones accounted for 52 per cent of the new cases. Both regions have closed schools in recent days, sending students online.

Mr Ford said his government will try to vaccinate teachers in those two regions more quickly, expand eligibility for vaccines in "high-risk areas" and organise mobile teams to give shots in residential buildings and large employers.

"I can't stress this enough. Things are extremely, extremely serious right now and moving rapidly," Mr Ford said on Wednesday.

The main variant spreading in Ontario - first detected in Britain - is 50 per cent more lethal than previous strains, health officials have said.

BLOOMBERG