First of caravan migrants reaches US border

Breakaway group of hundreds of Central American migrants travelling through Mexico to seek asylum in the United States have reached the Mexican border city of Tijuana.

United States military forces have reinforced security measures at the country's southern border, laying barbed wire and erecting barricades as migrants reached one of Mexico's northern-most cities.

The group of 400, who include LGBTQ migrants, broke away from the larger caravan of 5,000 people in Mexico City.

US Defence Secretary James Mattis said he would go to the US-Mexico border on Wednesday, which would be his first visit since the military announced that over 7,000 US troops would go to the area as the caravan of mostly Hondurans made its way through Mexico.

Larger groups are expected to arrive at the border in the coming days. The 5,000 migrants, who say they are fleeing persecution, poverty and violence in their home countries of Honduras, Guatemala and El Salvador, have largely been making their journey on foot.

The splinter group, which reached Tijuana on Tuesday, did so aboard a fleet of buses. Tijuana is at the westerly end of the border, about 38 kilometres from San Diego, California.

US Customs and Border Protection (CBP) said in a statement that it would close lanes at the San Ysidro and Otay Mesa crossings from Tijuana into California to allow the Department of Defence to install barbed wire and position barricades and fencing.

President Donald Trump has taken a firm stance against the caravan, which began its journey north on October 13 and briefly clashed with security forces in southern Mexico early on its route.

Trump signed a decree that effectively suspended the granting of asylum for those who cross the border illegally, a move that could drastically slow claims at gates of entry.

But migrants planning to seek asylum in the United States said they were undeterred by the crackdown.