A deadly blast of Arctic air that shattered decades-old temperature records as it enveloped the eastern United States has caused Niagara Falls on the US and Canadian border to become a winter wonderland that amazes visitors.

The cold weather caused the Niagara River to form an “ice bridge” and freeze over. Parts of the 53.6-metre American falls were covered in ice and the area below the observation area frozen over.

Large amounts of ice upriver from the falls led authorities to issue a flash-flood warning for two islands in the area, according to local media reports.

The low of -20.55 degrees Celsius at the National Weather Service office at Buffalo Niagara International Airport equalled a record that was set in 1942. Wind chill plummeted to -33.33 Celsius, The Buffalo News reported.

Record temperatures were caused when a polar air mass swept over North America during the past few days.

Authorities had put about half of the US under a wind chill warning or cold weather advisory notice.