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Frigid temperatures have sent parts of the Northeast into a deep freeze, including one of North America's most popular attractions: Niagara Falls.

Visitors to the falls that are on the border between New York state and Canada have over the past two days chronicled the halt of the usually running waters on social media.

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Tens of millions of people are under winter-weather alerts stretching from the Rockies to the Great Lakes region.

A storm that blanketed most of the Midwest with snow late last week headed east over the weekend, bringing bone-chilling temperatures to several areas including Boston, Pittsburgh and New York. Several spots saw a record-shattering chill, according to AccuWeather.

A woman walks past the frozen aftermath of a fire at the Morris Manor Apartments in Philadelphia on Jan. 22, 2019 Matt Rourke / AP

The blast of cold battered the Midwest and Great Plains with freezing temperatures and more than two feet of snow in some areas.

There were at least four storm-related fatalities including in Connecticut and Illinois as of early Tuesday.

A short reprieve is in the forecast in the Northeast, with "a dramatic rise in temperature later this week," said AccuWeather senior meteorologist Alex Sosnowkski.

But it will be short-lived.

After temperatures peak in the Northeast on Thursday, another blast of Arctic air is forecast to close out the week, AccuWeather said.