Agents reportedly fired tear gas as some migrants tried to break through a small hole in wire fences on the Mexican site of the frontier. Fumes were carried by the wind towards people hundreds of feet away.

“We ran, but the smoke always reached us and my daughter was choking,” said Ms Sarmiento.

A migrant family from Honduras runs from tear gas fired by US border patrol at Mexico border (Reuters)

The chaotic scenes unfolded after a large group of migrants began a peaceful march to appeal for the US government to speed up processing of asylum claims for Central Americans in Tijuana.

Mexican police kept them from walking over a bridge leading to a port of entry into the US, but migrants pushed past officers to walk across the Tijuana river below the bridge. They walked along the river to an area where only a bank of earth and concertina wire separated the migrants from US Border Patrol agents.

Some saw an opportunity to breach the border crossing, prompting US troops to fire several rounds of tear gas.

“We ran, but when you run the gas asphyxiates you more,” said Honduran Ana Zuniga, cradling her three-year-old daughter Valery in her arms.

Footage of the scenes provoked anger in the US.

“This is so incredibly shameful. Seeking asylum is not a crime,” said Black Lives Matter co-founder Alicia Garza. ”Shooting tear gas at asylum seekers lacks a basic level of humanity. This is your government. This is our government. Do not look away.”

Brian Schatz, a Democrat senator for Hawaii, said: “Anyone uncomfortable with spraying tear gas on children is welcome to join the coalition of the moral and the sane. We can argue about other stuff when we’ve got our country back.”

In a separate incident, a 26-year-old Guatemalan woman was injured after falling onto sharp fencing as she tried to enter the US with her two young children east of the San Ysidro port of entry on Friday.