Mayor of the US border town of Del Rio in Texas says 10,503 migrants, many of them Haitian, are waiting under a bridge that connects Mexico to the US, as they try to gain official entry into America.

Bruno Lozano claimed in a tweet Thursday night that the number had jumped by over 2,000 just during the day, and asked: "President Biden have you been briefed on the ongoing crisis yet?"

Reporters on the scene say migrants are telling them that some people have been wading through the Rio Grande River and back into Mexico to stock up on essentials, before heading back to the US side. They also say they have been given tickets from US border officials as they wait for processing.

The US Customs and Border Patrol (CBP) has announced it is beefing up its manpower at the border and is providing food, water, and portable toilets for the migrants and keeping them under the shaded bridge to prevent heat-related illness.

Republicans have been harshly critical of the Biden administration's response. Texas Senator Ted Cruz tweeted from the scene and wrote "This manmade disaster was caused by Joe Biden."

The Biden administration is also coming under intense criticism from defenders of the Haitian migrants. Although the Obama administration paused deportations of Haitians for over a year after a devastating Haitian earthquake in 2010, the Biden administration is not. And while nationals from Central America are allowed to remain in Mexico while they apply for US entry, Haitians are not afforded the same opportunity.

Figures from the CBP show a sharp jump in the number of Haitian migrants at the US border in the past year - over 29,000.

Haiti, long-suffering from economic woes, has been wracked again by upheaval recently. In July, President Jovenel Moise was assassinated and in August, a magnitude 7.2 earthquake killed and displaced thousands of people./aa