Thousands of asylum seekers have reached the southern United States border, as President Trump tries to prevent what he calls an "invasion".

Nearly six thousand troops have been deployed to the border.

US political scientist Mike Alison told Kate Hawkesby it's not yet known how many migrants, if any, will make it across the border.

"Many migrants have made the tough decision of deciding to return home, while some have taken up jobs in Mexico."

LISTEN ABOVE AS MIKE ALISON SPEAKS TO KATE HAWKESBY