The second migrant caravan, believed to be armed with bombs and guns, crossed into Mexico on Monday despite a huge police presence.
Hundreds of migrants following in the footsteps of the first caravan heading to the U.S. border crossed a river from Guatemala.
A low-flying police helicopter hovered overhead as the migrants waded in large groups through the Suchiate River's murky waters, apparently trying to use the downdraft from its rotors to discourage them.
Once on the Mexican side the migrants were surrounded and escorted by black-uniformed officers as sirens wailed.
The second group back at the Guatemalan frontier has been more unruly than the first that crossed. Guatemala's Interior Ministry said Guatemalan police officers were injured when the migrant group broke through border barriers on Guatemala's side of the bridge.
Mexico authorities said migrants attacked its agents with rocks, glass bottles and fireworks when they broke through a gate on the Mexican end but were pushed back, and some allegedly carried guns and firebombs.