'The town at the end of the universe': Desperate migrants willing to risk everything in Tapachula

Stuart Ramsay, chief correspondent, in Tapachula

A cloud of black wings rise into the air releasing a foul smell of rotting flesh.

A thousand vultures rest to earth and gorge on a new carcass thrown into a huge bin near a traveller shelter.

A child plays with a toy in the rubbish. A mother checks that her bag of belongings hasn't been stolen.

It is blisteringly hot.

This is Tapachula in southern Mexico. This is where the migrants come.

They wait for paperwork here. It's like the town at the end of the universe - but the US is less than a country away.

The insatiable desire to risk everything to get to the US is so acute here you can taste it. This is a transit point like no other I have seen.

Thousands every year, millions over time, have passed through and even contributed to this strange place. The residents are extraordinarily understanding.

Nobody is judged. They are passing through. They are going to America.

The travellers, who can afford it, meet their cartel gang handlers here. They have paid to be smuggled north through Mexico to the border with the US.

In Tapachula, they wait in line, applying for temporary Mexico residence permits. When they have the 15-day pass, they are free to move.

Without it they can be captured and deported by immigration officials.

They go legal in Mexico to travel illegally to the US.

This is a business worth millions - if not billions - and the gangs and cartels that facilitate the movement north use the same routes that they developed over years to move drugs.

Tapachula is a cargo hub: the cargo is humans.

A thousand miles to the north, Donald Trump is talking of putting the border under military control.

The 2,000 mile US-Mexico border isn't exactly easy to cross, but it is for large parts little more than a wire fence.

Knowledge of the crossing points is the key and the gangs divide it up between themselves.

In Tapachula, the Spanish-speaking south and central American travellers mix with nationals from across the globe.

One of the biggest groups attempting this journey come from Asia. Pakistanis, Indians, Bangladeshis and Afghans meet and eat in some of the now well known curry houses in the downtown district of Tapachula.

Africans hang out in hotels owned by "Papa Africa". They are from Sudan, Ethiopia, Ghana and the Ivory Coast.

The cartel guides tell me they pay off all the criminal groups to get their cargo north.

I asked who those groups are.

"The usual ones," he says.

"The federal police, local police, military, immigration, the cartels - the usual ones."

From the cargo hub in the south, to the northern entry point to the US, an enormous business is flourishing.

The cargo is humans.