Matías Romero (Mexico) (AFP) - Hungry and exhausted after three weeks walking across Mexico in a migrant caravan, Elsa Pineda implored US President Joe Biden to give her daughter a chance to escape the dangers of Honduras' gangs.

"He has to help those of us who really need it," she said after a night on a concrete floor near the side of a road with hundreds of other migrants.

Despite the perils of walking along busy highways through violence-plagued Mexico, sleeping outdoors at night, Honduras in comparison is "a thousand times" more dangerous, said Pineda, 35.

"Although we've faced hunger, rain and cold, thanks to God we're still here," she said.

But Pineda worries about her 15-year-old son, who she fears was taken away by immigration agents the night before.

As well as giving her eight-year-old daughter a chance at a better life, she also hopes to earn money in the United States to send home to her eldest daughter, who has just given birth.

The migrant crisis will be high on the agenda when Biden holds a three-way summit in Washington on Thursday with Mexican President Andres Manuel Lopez Obrador and Canadian Prime Minister Justin Trudeau.

Biden's arrival in the White House with a promise of a more humane approach towards migrants led to an increase in flows of undocumented foreigners fleeing poverty and violence.

But instead of the warm welcome they had hoped for, most have been turned away at the US border -- if they are not detained by the Mexican authorities along the way.

Bandages, walking sticks

Organizers of the caravan had initially intended to go to the capital to demand refugee status that would allow them to avoid deportation.

But they announced last week that the plan had changed and they would head to the US border instead, denouncing alleged mistreatment by the Mexican security forces.

Each night the mostly Central American migrants stop somewhere along the highway and spread out their blankets, plastic sheets or cardboard wherever they can find a place to sleep.

At dawn, they pack up their few belongings and carry them on their backs or in baby strollers.

Some wear flip-flops or flimsy sandals. Others hobble along using walking sticks, their feet chafed and bandaged after walking around 500 kilometers (300 miles) since leaving the southern border city of Tapachula on October 23.

One woman lay down by the side of the road, too tired or sick to go any further.

'Want to be free'

Struggling to keep up at the back of the caravan as organizers urged her to keep going, Erlinda Lopez made a plea to the US and Mexican presidents for help.

"We want to be free," she said.

Lopez, 31, fled Nicaragua with her 10-year-old daughter and 14-year-old son because of the "repression" that she said was rampant.

"All we want is to reach our destination (the United States) and raise our children," she said.

Tensions have been mounting between the Mexican authorities and the migrants following clashes and the killing of two Cubans last month.

The National Guard said its agents opened fire after the driver of the vehicle in which they were traveling ignored an order to stop and tried to ram a patrol vehicle.

Irineo Mujica, one of the caravan leaders, accused the Mexican government of treating the migrants like "animals."

"They don't see us as human beings," he told AFP.

At checkpoints along the route, immigration agents call out, offering the undocumented foreigners a one-year residency permit on humanitarian grounds.

While some have abandoned their march to accept the offer, others see it as a ploy to deceive and detain them.

They still have hundreds of kilometers to walk to reach the Mexican-US border, and security forces watch closely to ensure that passing motorists do not give them a ride.

"At times I feel like I can't go on but I know that I have to because there's no other way," said Lopez.

"I can't go back to my country," she said, wiping away a tear.