THE coldest, most ­dangerous blast of polar air in decades has gripped the US midwest and pushed toward the east and south and eastern Canada.

It closed schools and day care centres, grounded flights and forced people to pull their hoods and scarves tight to protect exposed skin from nearly instant frostbite.

Many across the nation went into virtual hibernation, while others dared to venture out in temperatures that plunged well below -18ÚC (0ÚF).

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"I'm going to try to make it two blocks without turning into crying man," said Brooks Grace, who was wrapping up to do some banking and shopping in Minneapolis, where temperatures reached -31ÚC (-24ÚF) with wind chills of -45ÚC (-48ÚF). "It's not cold - it's painful."

The mercury also dropped in Milwaukee, St Louis and Chicago, which set a record for the date at -27ÚC (-16ÚF). Records also fell in Oklahoma, Texas and Indiana.

Forecasters said some 187 million people in all could feel the effects of the "polar vortex" by the time it spread across the country yesterday.

Record lows were possible in the east and south, with wind chills expected to reach -23ÚC (-10ÚF) in Atlanta and -24ÚC (-12ÚF) in Baltimore.

From the Dakotas to ­Maryland, schools and day care centres shut down.

For a big swath of the midwest, the bone-chilling cold moved in behind another winter wallop - more than a foot of snow and high winds that made travelling treacherous.

Several deaths were blamed on the weather including a one-year-old boy who was in a car that went out of control and collided with a snowplough.