Parts of the US and Canada are braced for potentially record-breaking low temperatures as a blast of Arctic air blows across North America. A winter storm has already blanketed areas of Canada and the north-eastern US with up to 2ft (60cm) of snow.
Some 3,700 flights were cancelled on Monday, on top of thousands grounded over the weekend. Schools have been closed in several US states and residents urged to stay indoors for their own safety.
The storm and the deep cold have been blamed for 16 deaths in recent days.