TAPACHULA, Mexico (Reuters) - A migrant caravan of around 400 people, including many children, set off from the southern Mexican city of Tapachula for the United States on Saturday, just a couple of days after security and migration officials dispersed another large group.

       Mostly comprising Central Americans and Haitians, the caravan left at around 7:30 a.m. local time from a park in Tapachula where they had been staying, ignoring an earlier attempt by security forces to make them give up, a Reuters witness reported.

       Many in the group, which included Venezuelans and other South Americans, said they were fleeing poverty and violence at home as they began trekking towards the town of Huixtla.

       This week Mexican officials gradually broke up another caravan as President Andres Manuel Lopez Obrador said he wanted undocumented migrants to stay in southern Mexico, while also urging the U.S. government to help them find work.

       Sharon, a 31-year-old Honduran wearing a Minnie Mouse face mask, said after spending a year living in Tapachula struggling to support her three children by selling gum, she felt she had to make a bid to reach the United States.

       "I've handed in paperwork, but nothing ever gets fixed," she said tearfully. "Just appointments and more appointments. I am scared, but if I don't get out of here, I'm not going to get work," she said, declining to give her last name.

       Some of the migrants travelling in the caravan earlier this week complained they had been subject to brutal treatment by Mexican officials, and the government's National Migration Institute condemned incidents of violence captured on video.

       (Reporting by Jose Torres in Tapachula, Mexico; Editing by Dave Graham and Matthew Lewis)