A DEEP freeze has spread from the US midwest to the east and south, setting record low temperatures from Boston to Birmingham, and leaving 21 people dead.

The midwest and the east experienced temperatures colder than much of Antarctica. All 50 states have seen freezing temperatures, including Hawaii, where it was -8ÚC (18ÚF) on top of Mauna Kea, a dormant volcano.

The big chill started in the midwest over the weekend and has spread to cover about half of the country.

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In New York City, the high was expected to be -12ÚC (10ÚF), and in Boston, around -8ÚC (18ÚF).

Across the south, records were shattered like icicles. Birmingham, Alabama, dipped to a low of -14ÚC ( 7ÚF), breaking the record of -11.7ÚC (11ÚF) set in 1970.

The deep freeze dragged on in the midwest as well, with the thermometer reaching -24ÚC (-12ÚF) overnight in the Chicago area.

More than 500 passengers were stranded overnight on three Chicago-bound trains that were stopped by blowing and drifting snow in Illinois. Food ran low, but the heat stayed on.

The authorities reported at least 21 cold-related deaths since Sunday including five people who collapsed while shovelling snow.