Historic winter storm leaves nearly 50 dead across US

US emergency crews counted the grim costs of a colossal winter storm that brought Christmas chaos to millions, especially in hard-hit western New York, where the death toll reached 25 in what authorities described as a "war with mother nature."

Blizzard conditions continue to prevail in parts of the US Northeast, the stubborn remnants of a massive sprawl of extreme weather including severe cold that gripped the country over several days, causing widespread power outages, travel delays and at least 47 deaths nationwide.

The extreme weather forced the cancellation of more than 15,000 flights in recent days including more than 1,700.

Buffalo has been buried under staggering amounts of snow, with the National Weather Service forecasting up to 35 centimetres in addition to the several feet that have already left the city marooned, with a virtual collapse of emergency services.

"In addition to the 13 confirmed deaths, the Erie County Department of Health medical examiner's office has confirmed an additional 12 deaths, bringing the total for the blizzard to 25 deaths county-wide," Erie County executive Mark Poloncarz said in a press briefing.

The ferocious weather makes this "the worst storm probably in our lifetime, and the history of the city," Poloncarz said.

"This is not the end yet, we are not there," he said.

The extreme weather sent wind chill temperatures in all 48 contiguous US states below freezing over the weekend.