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.

Burying electrical wiring is more common in dense urban areas such as Toronto, but that doesn't mean they're immune to weather-related outages.