Tijuana, Mexico: United States officials closed a border crossing in southern California on Sunday (Nov 25) after hundreds of migrants tried to breach a fence from the Mexican city of Tijuana, US authorities announced.

The US Customs and Border Protection (CBP) office in San Diego, California, said on Twitter that it had closed both north and south access to vehicle traffic at the San Ysidro border post, before also suspending pedestrian crossings.

The incident took place only three days after US President Donald Trump threatened to close the ‘whole border’ with Mexico if ‘it gets to a level where we’re going to lose control or people are going to start getting hurt’.

Video clips posted on Twitter on Sunday showed large numbers of migrants dashing across a shallow concrete waterway towards the border. Several thousand migrants, mostly from Central America, have been gathering in Tijuana in hopes of entering the US.

At least 500 of them, including several women and children, had been taking part in a peaceful demonstration in Tijuana before dashing towards the border in an attempt to clamber over a first metal barrier there.

‘Are we in the United States yet?’ some asked in desperate tones.

Several hundred made it over the first barrier and were trying to cross a second - topped with spikes - when American border officers began firing tear gas at the group, even as US Army helicopters flew low overhead, according to an AFP journalist on the scene.

The migrants tried to protect themselves - covering their faces, with mothers holding their children close. There were cries of pain, desperation and frustration as the crowd swirled over the border line and back.

Some migrants shouted that they only wanted to make their way to a better life and find work in the US.

Amid the stinging gas, several migrants turned back, even as others tried to forge ahead.

Mr Trump has repeatedly warned that the large group of migrants moving through Mexico towards the US included criminals and possibly terrorists, while providing no evidence to support that.

He has deployed some 9,000 US troops along the border in support of the CBP agents.

Approximately 5,000 migrants reached Tijuana over the past week, after an exhausting trip of up to 4,000km covered in just over a month. Many were fleeing violence and poverty in Honduras, and hoped to find asylum in the US.

The San Ysidro border post is a busy one, with thousands of people passing through every day.