The Trump administration considered a proposal to mobilise as many as 100,000 National Guard troops to round up unauthorised immigrants, including millions living nowhere near the Mexico border, according to a draft memo obtained by The Associated Press.

Staffers in the Department of Homeland Security said the proposal had been discussed as recently as Friday.

The 11-page document calls for the unprecedented militarisation of immigration enforcement.

White House spokesman Sean Spicer said on Friday the document was "not a White House document".

"There is no effort to do what is potentially suggested," he said. Spicer called the AP report "100 per cent not true, adding that there was "no effort at all to utilise the National Guard to round up unauthorised immigrants".

A DHS official described the document as a very early draft that was not seriously considered and never brought to the secretary for approval.

Governors in the 11 states would have had a choice whether to have their guard troops participate, according to the memo, which bears the name of US Homeland Security Secretary John Kelly, a retired four-star Marine general.

While National Guard personnel have been used to assist with immigration-related missions on the US-Mexico border before, they have never been used as broadly or as far north.

The memo was addressed to the then-acting heads of US Immigration and Customs Enforcement and US Customs and Border Protection. It would have served as guidance to implement the wide-ranging executive order on immigration and border security that President Donald Trump signed January 25. Such memos are routinely issued to supplement executive orders.