Ontario's provincial utility says power has been restored to more than half a million customers four days after an ice storm first moved into the region, but that some hard-hit areas may remain without it until the end of the week.

Over 300,000 Canadians faced power outages in parts of Ontario on Sunday as an ice storm pummeled the region over the weekend, according to electricity provider Hydro One.

Some Ontario regions hard hit by last weekend's ice storm may not recover power until the end of the week, Hydro One said Tuesday as crews and communities braced for more freezing rain in the coming days.