The volunteers work for 23 hours following Santa, before racing home just in time for the delivery of their own presents.

First lady Michelle Obama is expected to volunteer, with calls forwarded to her on Christmas Eve.

Volunteers will field a growing number of calls from curious children from outside the US.

'We get a lot of calls from Europe, Australia and New Zealand,' said NORAD's Stacey Knott, who has organised the Santa tracking for three years.

While bilingual volunteers handle the foreign-language inquiries.

Normally the NORAD facility is responsible for defending the skies of the US and Canada and was originally located within Cheyenne Mountain in Colorado Springs in order to withstand a nuclear attack.

The tracking has now expanded into a large effort centered around noradsanta.org. Above, the website shows the dimensions of Santa's sleigh