The federal government's COVID-19 contact tracing app is facing criticism for its download requirements, which restrict some Canadians from accessing and using the app.

The free "COVID Alert" app, which became available on Friday, is designed to track the location of phones relative to each other, without collecting personal data anywhere centrally.

Users are notified if their phones have recently been near the phone of a person who later volunteers that they have tested positive for COVID-19.

But the app requires users to have Apple or Android phones made in the last five years, and a relatively new operating system.

Christopher Parsons, a senior research associate at Citizen Lab, part of the Munk School of Global Affairs and Policy, says that makes the app inaccessible for older Canadians and other marginalized groups.

Parsons says criticism should be directed at the federal government, not those who designed the app.

For a contact tracing app to properly work, he said, it requires 65 to 80 per cent of all Canadians to use it.

The current version of the app makes that impossible.

For now, the smart phone app is only linked to the Ontario health-care system, with the Atlantic provinces set to be the next provinces to link up.

Neither Apple nor Google returned requests for comment on the issue.