Tear gas fired at migrants trying to cross from Mexico

US agents fired tear gas and rubber bullets at hundreds of Central American migrants who climbed over a fence and attempted to rush the border from Tijuana, Mexico into the United States.

The San Ysidro border post -- the busiest crossing on the US-Mexico border -- was closed to north and south traffic and pedestrians for several hours following the incident on Sunday, the US Customs and Border Protection (CBP) office in San Diego, California said.

The migrants, mostly from Honduras, are part of a "caravan" loudly condemned by US President Donald Trump.

The shutdown took place only three days after 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."

Mexican Interior Minister Alfonso Navarrete accused some of the migrants of attempting to cross from Tijuana in a "violent way," and said they would be deported.

"Far from helping the caravan, they are hurting it," he told the Milenio television network.

Video clips posted on Twitter showed crowds of migrants dashing across a shallow concrete riverbed toward the United States. The sudden rush overwhelmed the outnumbered Mexican police, who were deployed with large clear shields and full riot gear.

Some 5,000 migrants have been gathering in Tijuana in hopes of entering the United States. Secretary of the US Department of Homeland Security (DHS) Kirstjen Nielsen accused the migrants of seeking to harm US border patrol personnel "by throwing projectiles at them."

"DHS will not tolerate this type of lawlessness and will not hesitate to shut down ports of entry for security and public safety reasons," she said in a statement, adding that US officials would "seek to prosecute" offenders.

At least 500 migrants, including women and children, had been taking part in a peaceful demonstration in Tijuana before dashing toward the border in an attempt to clamber over a first metal fence. "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 US border agents began firing tear gas and rubber bullets at them as US helicopters flew low overhead, an AFP journalist on the scene saw.

The migrants covered their faces to protect themselves from the acrid gas. Mothers clutched their young children close as they fled for safety. There were cries of pain, desperation and frustration as the crowd swirled into the riverbed and back.

Some migrants shouted that they only wanted to make their way to a better life. "They told us that if we crossed (the first barrier) they would give us asylum, because we were already in the United States," said Flor Jimenez, a 32-year-old Honduran woman. "But now it seems that they want to kill us, and we got very scared," said Jimenez.

She managed to reach the second border fence with her husband, her sister and her young daughter.

Amid the clouds of stinging gas, the crowd of migrants, including Jimenez and her relatives, fled back to Tijuana.

In a statement, the Honduran government "condemned" the use of rubber bullets and reiterated a request for United Nations assistance for migrants stranded on Mexico's northern border.

Trump has deployed some 9,000 troops along the border to support Customs and Border Protection agents.

Approximately 5,000 migrants reached Tijuana over the past week, after a trip of up to 2,500 miles (4,000 kilometers) covered in just over a month. Many said they were fleeing violence and poverty in Honduras hoping to find asylum in the US.

To enter the US legally, migrants must apply for asylum, but the wait for those requests to be processed can last up to a year.

Trump signed a proclamation earlier this month stating that asylum claims could only be filed at US ports of entry, but a federal judge in San Francisco temporarily blocked the order, pointing to "irreconcilable conflicts" with immigration law.

The Washington Post reported Saturday that the Trump administration gained support from the incoming Mexican administration of Andres Manuel Lopez Obrador -- who takes office December 1 -- for a plan to require asylum seekers to wait in Mexico for their applications to be processed.

But after that report was met by stiff criticism in Mexico, incoming administration officials said that the agreement was not yet final.

Incoming interior minister Olga Sanchez Cordero said in a statement that the new government's main goal is to make sure the human rights of the migrants are respected.