A blast of Arctic air is set to cover much of the United States with temperatures below freezing starting on Friday and into next week, impacting millions of Americans in nearly all of the contiguous states.

Americans were bracing Thursday for frigid temperatures that forecasters said could produce life-threatening conditions, with Donald Trump's inauguration expected to be the coldest in 40 years.

Intense snowy wintry weather in the US has been fuelled by activity of the polar vortex, slipping down to engulf large parts of the country. Early January's winter storm prompted seven states to declare states of emergency,

Temperatures are expected to plummet over the weekend, bringing life-threatening conditions to large stretches of the United States. The polar vortex will send temperatures below freezing for much of the country starting this weekend and stretching into next week,

Despite a cold start to the day, most of the U.S. will experience seasonably mild temperatures on Thursday. However, dangerous changes are on the way as a polar vortex tightens its grip on the nation as sends temperatures tumbling below freezing starting this weekend.