The first 100 troops have arrived at the US-Mexico border to await the arrival of the migrant caravan slowly making its way north from Central America.

On Thursday, 109 troops from the 591st Military Police Company were taken from Fort Hood, Texas, to to Lackland Air Force Base to help with operations there. 

Separately, troops stationed at the Fort Huachuca base in Sierra Vista in Arizona were seen setting up tents for comrades who are due to arrive over the weekend and in the coming weeks. 

President Trump has vowed to send as many as 15,000 troops to tackle the three migrant caravans which are snaking their way through Mexico towards the U.S.

He said he will make 'tent cities' to keep migrants once they are detained but it is not yet clear where those will be. 

The plan, he said, is to 'end catch and release' by keeping the migrants there to face trial once they are caught. 

'We're going to catch, we're not going to release,' he said on Wednesday in a lengthy speech where he also threatened that any migrants who throw stones at soldiers will be shot.