(Reuters) -Ontario will begin a four week-long stay-at-home order and close in-store shopping for non-essential retailers as of Thursday, Premier Doug Ford said on Wednesday, as the Canadian province battles a surge of COVID-19 cases.

“The situation is extremely serious. We need to hunker down right now,” Ford said at a briefing in Toronto.

“What we do until we start achieving mass immunization will be the difference between life and death for thousands of people.”

The order requires people in Canada’s most populous province to stay in their residences except for essential reasons, including exercise, vaccination appointments or grocery trips.

Last week, Ontario shuttered all indoor and outdoor dining, a move that fell short of what the government’s expert advisory panel said was necessary to avoid catastrophically high case numbers.

All retailers except those selling grocery, pharmacy and gardening goods will close for four weeks, except for curbside pickup. Big box stores can remain open, but with capacity limits and only certain products including groceries, pharmacy and gardening materials available for in-store purchase.

Industry groups had criticized Ford for allowing big box stores to remain open during past lockdowns while shutting small businesses.

Retailers considered essential can open for in-store shopping by appointment only. These include medical device supply and repair shops, optical stores and auto mechanics.

On Tuesday, Canada reported 6,520 cases, the most recent data publicly available. Prime Minister Justin Trudeau warned of a “very serious” third wave of the virus, with more young people going into hospital and on ventilators due to more lethal variants.

Hospitals in Ontario are becoming more stretched. Provincial data showed more COVID-19 patients in intensive care units than at any point since the pandemic began.

ICU admissions are rising faster than the worst-case scenario modelled by experts, Ford said.

The province also announced that all teachers and education staff in Toronto and the suburb of Peel would be eligible for vaccination beginning during the school districts’ April break.

On Tuesday Toronto Public Health shuttered the city’s schools for in-person learning, sending the country’s largest school district of around 247,000 students back to remote learning from Wednesday until April 18.

Hours earlier Ford had told reporters that schools were safe and closures would be unnecessary.

Ontario reported 3,215 new cases on Wednesday, according to government data.

(Reporting by Moira Warburton in Vancouver Editing by Chris Reese and David Gregorio)