CNN reports Mexican police in riot gear pushed them back, setting off smoke canisters, and Buzzfeed reports the use of tear gas.

Hundreds of Mexican Federal Police sealed the border as drones and helicopters hovered above the crowd, whichwaited on a bridge in sweltering heat...

The chaos calmed somewhat as migrants formed lines in a mass of humanity stretching across the bridge.Some returned to the Guatemalan side to buy water and food.

"Today, violent tides are trying to enter Mexico and they have hurt Mexican police. We did not use armed forces because we offered the obligation to help, " Mexican Interior Secretary, Alfonso Navarrete Prida told Mexican Milenio television.

At least a dozen migrants stuck on the bridge have jumped into the river below.