Winter continues to wreak havoc in much of Canada, as a sudden mass outage sends some 100,000 Newfoundlanders back in the dark while a wide swath of the Prairies is enveloped by extremely cold, dense air.

Power outages across Newfoundland worsened Sunday night after a sudden problem at the trouble-plagued generating station in Holyrood, southwest of St. John's. 

Dawn Dalley, a vice-president with Crown-owned Nalcor Energy, said there appears to have been a problem with the Holyrood plant's switchyard.

About 100,000 customers immediately lost power around 9:30 p.m. NT. Power was soon restored to some customers. More have been gradually brought back on line. 

Numerous people reported seeing a green flash or heard what some assumed was an explosion.

Newfoundland and Labrador Hydro confirmed via Twitter that there was "a flash" and "a bang" at its Holyrood generating station, but there was no explosion or fire. All workers are safe, the tweet also said.

Power troubles for Newfoundlanders began on Saturday after a fire at a substation caused an outage at the Holyrood station at around 9 a.m., throwing much of the island into darkness.

There were 190,000 without power at the peak of the outage.

Newfoundland Power, the private company that supplies much of Newfoundland and Labrador Hydro's energy to consumers, has also been conducting rolling blackouts to keep the power grid intact since Thursday.

While hydro companies work to restore power, Newfoundlanders are being asked to conserve energy, such as not running the driers or the dishwashers. They have also been warned that the conservation effort could go on for weeks while the system stabilizes, according to CBC reporter Peter Cowan.

Meanwhile, many gas stations were out of gas or didn't have the power to pump it, Cowan reported. Some store shelves were also picked clean.

Speaking with reporters on Sunday afternoon, Newfoundland and Labrador Premier Kathy Dunderdale said the situation is not considered a crisis.

Several flights were cancelled in St. John's and the city announced it was opening a warming centre after roughly half the island lost power. Other municipalities opened public buildings for people needing warmth as some coped with digging out from as much as 40 centimetres of snow.  

Prairies in deep freeze

Meanwhile, much of Saskatchewan and Manitoba are under extreme wind chill warnings, where residents are shivering through temperatures in the –40s C — feeling closer to –50 C in the wind.

The potentially record-low temperatures are heightening fears of frostbite and hypothermia.

The deep freeze in the Prairies is nothing new to residents of Winnipeg who have been hearing about frostbite warnings for four weeks now. The kind of cold people are experiencing can freeze skin in under 10 minutes.

One of the coldest places in Canada on Saturday night was Newfoundland, which was hit with a strong blizzard Friday, followed by wind chills that made it feel like –30 C.

St. John's Mayor Dennis O'Keefe said Sunday he is recommending that schools and post-secondary institutions be kept closed until at least Wednesday.

"It gives us, as a city, time to get out there and deal with the streets and deal as much as we can within the next few days with sidewalks and everything else," he said.

He also recommended that people help out by "shovelling out the catch basins" as the province is due for heavy rain and warmer temperatures.

"That brings another challenge," O'Keefe told CBC News in an interview Sunday afternoon. "Whether there will be possible flooding in neighbourhoods."

O'Keefe also said he's worried about the swing in temperatures and mixed precipitation which could load down the transmission lines with ice and trigger another round of massive outages.

'Flash freeze' for parts of Central Canada

Elsewhere in the country, people in southern Ontario are bracing for another snow storm. Snow is already falling in some areas but it is expected to intensify later in the day and into Sunday night.

Some areas will be hit with mixed precipitation. Toronto and the Ottawa region are under a freezing rain warning. Areas northwest of both cities could see anywhere from 10 to 20 centimetres of snow.

CBC Meteorologist Janine Baijnath warned of a "flash freeze" in the Toronto area in the wake of freezing rain, which could cause transportation problems among other things.

Wind chill warnings are in effect for northwestern Ontario, as another blast of Arctic air invaded the region Saturday night. Temperatures are expected to plummet to –30 C to –35 C. With wind chills, it will feel more like –40 C Saturday night and into Sunday morning.

Freezing rain warnings have also been issued for most of eastern Ontario for Sunday evening and into Monday morning.

Across much of Quebec, the extreme cold has given way to warmer temperatures. However, now there is a freezing rain warning in effect for the southern and central parts of the province just as many people get back on the road at the end of the holiday season.

South of the border, bitterly cold temperatures blowing into the U.S. Midwest and Northeast in the coming days are likely to set records.

About 1,300 flights had been cancelled Sunday at O'Hare and Midway international airports in Chicago, aviation officials said, and there also were cancellations at Logan International Airport in Boston and Tennessee's Memphis and Nashville international airports.

The frigid air began Sunday and was expected last for at least two more days. The cold mass of air could be funnelled as far south as the Gulf Coast because of what one meteorologist called a "polar vortex," a counterclockwise-rotating pool of cold, dense air.