US President-elect Donald Trump has doubled down on his campaign promise of the mass deportation of illegal immigrants, saying the cost of doing so will not be a deterrent.

In some of his first public remarks since winning the election, Trump said his priority upon taking office in January would be to make the border "strong and powerful". "It's not a question of a price tag.

It's not - really, we have no choice," Trump told NBC News.

But how would Trump's campaign pledge of mass deportations of migrants actually work and what are the hurdles he may face?