Fox News host Tucker Carlson has described the arrival of about 500 African migrants at the US border in the space of a week a “flood” that could become a “torrent”.

The number is unusually high for African nationals trying to enter the US on the southern border, roughly double the number detained by Border Patrol during the whole 2018 financial year. However, it is a fraction of the 33,000 people apprehended since the start of the year at the US border, according to the US fact-checking site Snopes.

Mr Carlson said: "It’s going to overwhelm our country completely.”

“We are continuing to see a rise in apprehensions of immigrants from countries not normally encountered in our area,” said Raul Ortiz, head of the US Border Patrol’s Del Rio sector.

Reports suggest they are mostly from the Republic of the Congo, the Democratic Republic of the Congo and Angola and flew to South America before embarking on their journey northward.

About 300 hundred of the African migrants were recently released in San Antonio, Texas, which has a population of 1.5 million. Another 200 travelled to Portland, Maine, which has about 66,000 residents.

“The population growth in that part of the world, particularly in the continent of Africa suggests that this flood could become a torrent,” Mr Carlson said, as his network aired pictures of migrants in Peru, about 3,000 miles away from the US border.

His guest, Andrew Arthur of the Center for Immigration Studies (CIS), seemed to agree. Despite the normalising name, the Center for Immigration Studies is listed as a “hate group” by the Southern Poverty Law Center, and Mr Arthur has recently written articles mocking climate refugees and saying the US needs a border “czar”. The CIS has filed a lawsuit against the Southern Poverty Law Center over its claims.

Mr Arthur claims one woman had told the New York Times she was penniless.

But while the article does quote her saying this, it also describes the woman saying with tears in her eyes that she had been attacked and raped during the journey.

News of the arrival of the migrants sparked rumours on social media that some were carrying the ebola virus, although officials in both San Antonio and Portland said these were unfounded.

“We do not have any suspected or confirmed cases of ebola right now in Texas,” Lara Anton, spokeswoman for the Texas Department of State Health Services, told Snopes.

Ethan Strimling, the mayor of Portland, denied that the migrants constituted a "crisis" and said a donation campaign in the town had raised $20,000 for them in the first 36 hours.

He told the New York Times: "I don’t consider it a crisis, in the sense that it is going to be detrimental to our city. We’re not building walls. We’re not trying to stop people. In Maine, and Portland in particular, we’ve been built on the backs of immigrants for 200 years, and this is just the current wave that’s arriving."

Late on Monday night, US President Donald Trump also promised to begin deporting “millions” of people living in the US illegally.