OTTAWA -- Up to five million Canadians are expected to use mail-in ballots rather than show up in person to vote on Sept. 20 in the midst of a fourth wave of COVID-19.

In the last election just over 50,000 people chose the mail-in option, most of them Canadians who were out of the country and had no other choice.

For Canadians in the country there are other options, including four days of advance polls and voting in person at any time in any of Elections Canada's 501 offices across the country.

But for those who are thinking of using the mail-in option this time, it's important to plan ahead.

Here's what you need to know:

-- You can apply online or at any Elections Canada office for mail-in ballot kits. The deadline for applications is 6 p.m. on Sept. 14. But keep in mind that once you apply, you cannot change your mind. You cannot vote in advance polls or cast an in-person ballot on election day.

-- If you are voting while out of the country or outside of the riding in which you normally reside, your mail-in ballot must be sent to Elections Canada headquarters in Ottawa and received by 6 p.m. on Sept. 20. Your vote will apply to the riding in which you normally live or in which you last resided.

-- If you are voting by mail in the riding in which you live, you have until polls close in your location to get your ballot to your local returning office. If you are worried that a mailed ballot won't be received in time, you may drop it off at a polling station on election day or have a friend or family member do it for you.

-- If you don't receive a ballot kit or lose it, you may go to your local polling station on election day and swear an oath to that effect. You will then be allowed to vote in person.

However, Elections Canada will be checking, through bar codes on the envelopes containing mail-in ballots, to ensure no one votes twice. If elections officials subsequently discover that you did in fact send in a mail-in ballot, that ballot will not be counted.

More information on voting by mail can be found on the Elections Canada website.

This report by The Canadian Press was first published Aug. 18, 2021.