The polar vortex of cold air from the Arctic has partly frozen the Niagara Falls, the US side of which is shown here after being photographed from Ontario in Canada on Wednesday. (Reuters and AP pictures)

Spectacular and intricate formations of twisted icicles can be seen after the sides of the three waterfalls that plunge 170 feet on the American-Canadian border have turned to ice

In some segments, water is still flowing as millions of tourists have seen it earlier. Tourists will need to hurry if they are to witness the icicle spectacle as forecasters say that the vortex is retreating north again

In case you manage to cross continents on time, don’t miss this postcard view of frozen mist from the Niagara Falls coating the landscape around Prospect Point at the state park. But be warned: it is so cold that in Kentucky, an escaped convict begged to be let back into prison — and presumably strip-searched — after nearly freezing to death as he hid in a derelict house.