A warning from America's former immigration bos, about the dangers of closing the US border with Mexico.

Donald Trump is stepping up his threats to close part or all of the border.

He says he'll be forced to take action, if Congress doesn't fix immigration and security loopholes immediately.

Former Director of US Citizenship Immigration Leon Rodriguez told Kate Hawkesby such action would have devastating consequences, particularly in border cities and towns.

"There's people going back and forth across the border, to go to school, not to mention all kinds of merchandise, all kinds of raw materials, also go back and forth."

Some commentators have accused Trump of making empty threats he won't act on, but Rodriguez says Trump's threats need to be taken seriously.

"I could very well see that he may not be bluffing, that he may go through with this, at least temporarily."