Mega migrant caravan from dozens of countries begins marching towards the US amid fears Trump will close the border if he returns to the White House

A major migrant caravan is making its way towards the United States, hoping to reach the southern border before the November election out of fear that if former President Donald Trump wins, he may close the border.

'We are running the risk that permits [to cross the border] might be blocked,' said Miguel Salazar, a migrant from El Salvador. 

He said he worried that a new Trump administration might stop granting appointments to migrants through CBP One, the app migrants use to enter the US legally — by getting appointments at U.S. border posts, where they make their cases to officials.

The app only works once migrants reach Mexico City, or states in northern Mexico.

It is unclear exactly how many migrants - from dozens of different countries - are involved in the caravan, but it is estimated to be anywhere from several hundred to 1,500 or more, according to Breitbart.

The group left Sunday from the southern Mexican town of Ciudad Hidalgo, next to a river that borders Guatemala.

Some said they had been waiting in the city for weeks, for permits to travel to towns further to the north.

Among them was Oswaldo Reyna, a 55-year-old Cuban migrant who crossed from Guatemala into Mexico 45 days ago, and waited in Ciudad Hidalgo to join the new caravan - which was announced on social media.

He criticized Trump's recent comments about migrants and how they are trying to 'invade' the United States.

'We are not delinquents' he said. 'We are hard working people who have left our country to get ahead in life, because in our homeland we are suffering from many needs.'

Other migrants are also expected to join the caravan as it travels further north. 

Migrants trying to pass through Mexico in recent years have organized large groups to try to reduce the risk of being attacked by gangs or stopped by Mexican immigration officials as they travel. 

But the caravans tend to break up in southern Mexico, as people get tired of walking for hundreds of miles.

Recently, Mexico has also made it more difficult for migrants to reach the US border on buses and trains.

Travel permits are rarely awarded to migrants who enter the country without visas and thousands of migrants have been detained by immigration officers at checkpoints in the center and north of Mexico, then bused back to towns deep in the south of the country.

Yet the country has also provided police escorts to the migrants in the past, and provided them with shelter, food and beverages.

It remains unclear whether the Mexican government will assist this caravan.