US agents have reportedly fired tear gas at migrants as some attempted to breach the border separating Mexico and the United States.

The Associated Press reported that migrants approaching the border wall in Tijuana, Mexico, were enveloped in smoke.

US agents shot the gas, according to an AP reporter on the scene. Children were heard screaming and coughing in the mayhem, it said.

Honduran migrant Ana Zuniga, 23, told the news agency that she saw migrants open a small hole in concertina wire at a gap on the Mexican side of a levee, at which point US agents fired tear gas at them.

“We ran but when you run the gas asphyxiates you more,” she told the AP while cradling her three-year-old daughter Valery in her arms.

Mexico’s Milenio TV also showed images of several migrants at the border trying to jump over the fence.

A few yards away on the US side, shoppers streamed in and out of an outlet.

US Border Patrol helicopters flew overhead, while agents held vigil on foot beyond the wire fence in California.

The Border Patrol office in San Diego said via Twitter that pedestrian crossings have been suspended at the San Ysidro port of entry at both the east and west facilities.

Earlier on Sunday, some Central American migrants pushed past a blockade of Mexican police who were standing guard near the international border crossing.

They appeared to easily pass through without using violence and some of the migrants called on each other to remain peaceful.

A second line of Mexican police carrying plastic riot shields stood guard outside a Mexican customs and immigration plaza.

That line of police had installed tall steel panels behind them outside the Chaparral crossing on the Mexican side of the border.

US President Donald Trump has raised alarms about the caravan as it approached the US, and has deployed military forces to the border to support the Border Patrol.

Trump tweeted on Saturday that migrants at the border would stay in Mexico until their asylum claims were individually approved in US courts, but Mexico’s incoming government denied they had struck any deal.