The Omicron patient is a 51-year-old who travelled from South Africa, according to a Friday post on Twitter from Deputy Health Minister Hugo Lopez-Gatell, who added the person has presented only mild symptoms so far.

"Their likelihood of recovery is favourable," Lopez-Gatell wrote.

The Mexican case follows the discovery of the variant in Brazil earlier this week, its first known appearance in Latin America, a region particularly hard hit by the pandemic over the past two years.

Brazilian health authorities confirmed Omicron in three persons who had travelled to South Africa and Ethiopia.

In Mexico, the infected person arrived at the Mexican capital on November 21, and six days later presented symptoms of the highly-contagious respiratory disease, according to a health ministry statement.

The patient was treated at a private hospital in Mexico City on November 29, and is in "voluntary preventative isolation," the statement said.

Lopez-Gatell, the public face of Mexico's COVID-19 policies, said closing borders was not a useful tool to contain variants, and that people should not overreact to the presence of new virus variants circulating in the country.

"We call on all to stay calm and keep applying measures to avoid the spread of infection," he said, citing vaccination and the use of face coverings.

President Andres Manuel Lopez Obrador also attempted to tamp down concern over the Omicron variant at his regular morning news conference on Friday.

"One of the things about this variant, as of right now, is that it isn't (more) damaging, it isn't more dangerous than other variants," he said.

On Friday, the World Health Organisation's chief scientist urged people not to panic over the emergence of the variant, and said it was too early to say if vaccines would be need to be reworked.

Australian Associated Press