The full effect of an ice storm that derailed transit and left thousands in the dark overnight has not yet been realized, city officials warned.

Freezing drizzle that was expected to build up overnight while temperatures dropped and winds gusted may continue to spell disaster for heavy tree limbs and already coated power lines after a full day’s clean-up was set in motion Sunday.

“Nature is not going to help us get rid of this,” said senior Environment Canada climatologist David Phillips. “This is truly the nightmare before Christmas.”

After 264,000 customers were reportedly without hydro in Toronto on Sunday, and almost another 200,000 across the GTA and beyond, residents are being warned to prepare for as many as 72 hours in the dark — with the risk many may still not have power for the holidays.

“Hydro expects the worst weather still to come,” Mayor Rob Ford told a news conference Sunday afternoon. “If it gets really bad in the next 24 hours we could have a state of emergency, but I don’t want to say that right now. We’re not in that situation quite yet.”

The situation heading into Monday was a fractured transit system, water pumping stations out of commission, cancelled flights and a large portion of the city’s most vulnerable left without electricity and heat in community housing.

Ford said his own Etobicoke home is without power and that his family may have to stay at a hotel tonight.

“This is one of the worst storms in Toronto’s history,” he said.

Phillips said the total amount of freezing rain has not yet been calculated, but it could set a record.

“I think this will stand out to be one of the longest bouts of freezing rain in Toronto,” Phillips said, adding there has been at least 40 hours of rainfall recorded at Pearson International Airport since the storm began — twice the annual average amount.

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Winds were expected to reach speeds as high as 40km/hr headed into Monday, Phillips said. Temperatures are forecasted to reach a high of only minus-3C by Christmas Eve, meaning the ice likely won’t get a chance to melt.

“That puts a lot of stress on the wires and cables,” Phillips said. Even though the famous 1998 ice storm in eastern Ontario and Quebec was one of the worst recorded, there were minimal winds, he said. Ice continuing to coat tree limbs adds extra complications.

“When the system moves away the cold air rushes in and that’s when people really freeze in the dark.”

As Torontonians rushed to make emergency preparations, one downtown Home Depot location confirmed most stores across the GTA were sold out of generators. Some without power at home headed to shopping malls, but there were no guarantees there either as several complexes, including the Shops at Don Mills and the Pickering Town Centre, were closed without electricity.

Crews worked to restore power after more than 90 large-scale outages, Toronto Hydro said. The company advised customers that full restoration could take up to 72 hours.

All available forestry staff were working to clear trees along with hydro employees, Toronto Hydro CEO Anthony Haines said, adding the number of calls reporting outages was increasing every minute.

“We continue to be really in the middle of the storm,” Haines said. “The damage continues to be done as we speak. “We will not rest until such time as we’ve fixed it.”

Toronto Fire said they received hundreds of calls for downed power lines and expected a high volume of calls to continue throughout Sunday.

Toronto Police said they called in all available personnel and asked citizens not to drive unless “absolutely necessary.”

Both Sunnybrook Hospital and Toronto East York General Hospital were running on backup generator power Sunday. Ford said those locations would be made a priority.

Six premature newborns were evacuated from Sunnybrook a precaution on Sunday morning.

Craig Dumahel, a spokesperson for Sunnybrook, said scheduled surgeries were going ahead as planned.

There were also 20 Toronto Community Housing buildings without power Sunday, Ford said, affecting thousands of residents.

As the city advised residents to stay home during one of the busiest weekends in travel, transit in and out of major hubs and across the downtown core experienced massive delays and complete shutdowns as the ice stalled many modes of rail — leaving trees on the tracks and subway stations without power.

TTC CEO Andy Byford said the biggest challenge going into the week is the inoperable streetcar system, which remained unchanged Sunday. Ice coating the copper wires that provides power to the cars was too thick to cut through, Byford said.

“They just could not get through,” Byford said Sunday. The TTC’s strategy shifted to keeping the subway running and providing bus shuttles, he said. If the weather didn’t allow for the ice on the wires to melt, there would a “real chance” the streetcars would remain off the roads on Monday, Byford said.

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The Sheppard subway line and the Scarborough RT line were also suspended throughout Sunday. Various stations on the Yonge-University line were experiencing power issues affecting service that caused trains to turn back.

There were shuttle buses running in affected areas, thinning regularly scheduled routes as vehicles were redeployed, Byford said.

Both the Lakeshore West and East GO train lines were experiencing delays after the East trains were earlier suspended because of power issues. GO bus service experienced delays as long as 40 minutes.

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VIA Rail said their service was continuing, but delays should be expected on the Toronto-Ottawa, Toronto-Montreal and Toronto-New York lines.

More than 170 flights were cancelled at Pearson, including trips to Chicago, New York and Vancouver. Travellers were advised to check their flight status before leaving home.

The F. J. Horgan water treatment plant, the newest of the city’s facilities in the city’s east end, had been out of commission since just after midnight, said general manager of Toronto Water Lou Di Gironimo. There were also some pumping stations out of order.

Di Gironimo said there was enough water in the city’s reservoirs that the impact of the failing stations wouldn’t be felt for at least another day or two.

Some people in high rises might experience water supply issues if their building relies on booster pumps — individual to the private buildings — to get water to higher floors, he said.

There were no significant issues with water main breaks or sewer overflow Sunday, Di Gironimo said.

Deputy Mayor Norm Kelly said Sunday he is “coping” just like everyone else.

“This is the universe putting us in our proper place,” Kelly joked Sunday afternoon. He said tree branches had been cracking and falling around his Scarborough home since Saturday.

He said there has been an “avalanche of phone calls,” at the emergency operations centre from across the city, Kelly said. The city’s website was down for most of the day, as staff tweeted from official accounts.

“They’re doing their very best.”

City staff said an emergency could be declared if there are powers, resources and money needed that isn’t already available.

Ford — who was earlier stripped of his emergency powers by council — could declare or end an emergency, but all authority during an emergency situation now belongs to Kelly.

Kelly said he spoke to Premier Kathleen Wynne, who offered to assist if necessary.

Normally the city would be able to request the help of emergency crews from outside jurisdictions, Kelly said, but the storm’s scope means that support is not readily available.

“All available resources are working to keep you and your families safe,” Wynne told a press conference. “We’ve offered our full support and our assistance.”

The province’s emergency management staff are in contact with the municipalities, Wynne said. In some areas, crews moved in preemptively to affected areas.

“Christmas is just a few days away, and we are doing everything possible to restore power and ensure safety,” she said.

Prime Minister Stephen Harper also sent words of encouragement Sunday afternoon, tweeting: “Thoughts are with those without power due to the ice storm — please stay safe.”

There have been no deaths or serious injuries reported.

Peel Regional Police said a 10-year-old boy was taken to hospital after being hit by a falling tree branch. The child’s injuries were not life-threatening, police said.

There is not yet a cost estimate of storm damage and cleanup, Ford said.

Officials asked residents to keep non-perishable food and water on hand, check on elderly neighbours and keep children and pets indoors.

Citing weather concerns, both Toronto school boards cancelled all permits and closed all facilities including daycare for Monday.

There are several community centres open 24 hours. They include: Dennis R. Timbrell Resource Centre (29 St. Denis Dr.); Malvern Community Centre (30 Sewells Rd.); Agincourt Community Centre (31 Glen Watford Dr.); Don Montgomery Community Centre (2467 Eglinton Ave. E) Driftwood Community Centre (4401 Jane St.); Mitchell Field Community Centre (89 Church Ave.); and Joseph J. Piccininni Community Centre (1369 St. Clair Ave. W).

With files from Andrew Nguyen, Paul Clarke and Joel Eastwood