TORONTO -- The Ontario government is asking Ottawa for enhanced measures for interprovincial travellers as the province grapples with skyrocketing hospitalizations and cases of COVID-19 variants.

In a letter Monday to the federal ministers of health and public safety, Ontario says it has already closed its boundaries with Quebec and Manitoba to non-essential travel, but there are no measures in place to protect provinces from the spread of COVID-19 variants through interprovincial air travel, an area of federal responsibility.

The province is asking for mandatory pre-departure PCR testing for all domestic air travellers entering Ontario, an extension to current rules for international passengers seeking entry into Canada.

The letter, which was shared with The Canadian Press, says there have been 17 domestic flights in the past two weeks to Toronto's Person International Airport with possible COVID-19 exposures.

It adds there have also been potential exposures on flights landing at other Ontario airports, including Ottawa and Hamilton.

The letter comes as health-care workers from Newfoundland and Labrador are set to arrive in Ontario today, as well as three teams of nurses and medical technicians from the Canadian Armed Forces.

It says limiting mobility is a key factor to reducing the risk of further spread of COVID-19 variants.

"Over 70 per cent of daily cases in Ontario have been confirmed as variants of concern," says the letter signed by Ontario Health Minister Christine Elliott and Solicitor General Sylvia Jones.

"These variants entered through our borders, both international and domestic, and it is critical that every effort is made to keep them out."

The letter says it is crucial that the transport of essential goods is not hindered by border measures, but "it is likewise crucial that all non-essential travel be curtailed."

"The introduction of stricter pre-departure testing measures, in addition to providing an extra layer of protection for interprovincial travellers, is a significant step to achieve that goal and ensure that collectively we are doing all we can to protect our citizens," the letter reads.

"These new measures should be in place for as long as necessary, or until the risks of new variants in Canada have been effectively minimized."

This report by The Canadian Press was first published April 27, 2021.