Denver Mayor Michael Hancock has apologized after urging citizens to avoid travel, then hopping on a flight to see his own family in Mississippi.

Hospitalizations, deaths and the testing positivity rate are also up sharply as the nation approaches Thanksgiving, and public health experts have warned that the large family gatherings expected for the holiday are likely to extend and exacerbate the surge.

Trump's 2018 joke about a turkey disputing the results of a vote is recirculating amid his efforts to do the same.

At Denver International Airport alone, about 25 centimetres of snow mixed with winds that limited visibility prompted the cancellation of about 30 per cent of the airport's average daily 1,600 flights.

Black Friday shopping, the annual rite of passage on the day after Thanksgiving, continues to creep further into the holiday as more stores open their doors a day early.