About 3,500 migrants, the majority of them Central Americans, are stranded and facing an emergency situation in Coatzacoalcos, a city in the eastern Mexican state of Veracruz, due to the derailment of a train and a bridge collapse, a non-governmental organization said.

"The migrants, among whom there are some pregnant women, children and sick people, face the risk of contracting skin, eye, gastrointestinal and respiratory diseases since they are living, eating and sleeping a few steps from where many people are defecating and urinating," the Mesoamerican Migrants Movement, or MMM, said in a statement.

The train known as "The Beast," which is used by many Central Americans to reach central Mexico on the long trek to the United States, derailed on June 17 between Medias Aguas and Tierra Blanca.

Thousands of migrants continue arriving in Coatzacoalcos and are in need of food and medical assistance as they wait to resume the journey north.

State and municipal officials have been overwhelmed by the huge number of migrants, who have not been detained or deported.

Hundreds of migrants have poured out of the city on foot, walking north amid high temperatures in search of trains heading to northern Mexico, the MMM said.

"Four hundred migrants are walking from Coatzacoalcos to Acayucan with the hope of reaching Tierra Blanca," a trek of about 300 kilometers (186 miles), MMM member Marta Sanchez Soler, who has been helping the migrants, told Efe.

The Central Americans are avoiding buses so they will not be caught by Mexican immigration agents, leaving themselves vulnerable to abuse by gangs and people traffickers, the MMM said.

At least 60 migrants have been surrendering daily to the National Migration Institute, or INM, out of desperation, the non-governmental organization said.

The MMM is one of many non-governmental organizations that have been providing assistance to the Central Americans over the past two weeks.

Federal, state and municipal officials, working with the Red Cross, have started building latrines in the area, as well as places where people can bathe and wash clothes.

The Veracruz Water Commission installed a potable water station in the area, while the Coatzacoalcos city government is distributing supplies to the migrants.

An estimated 300,000 Central Americans undertake the hazardous journey across Mexico each year on their way to the United States.

The trek is a dangerous one, with criminals and corrupt Mexican officials preying on the migrants.

Gangs kidnap, exploit and murder migrants, who are often targeted in extortion schemes, Mexican officials say.

Central American migrants follow a long route that first takes them into Chiapas state, which is on the border with Guatemala, walking part of the way or riding aboard freight trains, buses and cargo trucks.

The flow of migrants has increased markedly in the northern and northeastern parts of Mexico since U.S. officials increased security along the border in the northwestern part of the country.

A total of 46,716 Central Americans were deported from Mexico between Jan. 1 and Nov. 30, 2011, the INM said in a report released earlier this year.

The majority of the migrants - 41,215 - were men and nearly half, some 23,560, were from Guatemala, the INM said. EFE