Mexico's deputy health secretary said measures such as restricting travel or closing borders are of little use in response to the emergence of the new Omicron coronavirus variant.

Hugo Lopez Gatell, who has been the face of the Mexican government's response to the pandemic, said some of the measures other countries have taken are "disproportionate" to what the existing scientific evidence shows.

"It has not been shown to be more virulent or to evade the immune response induced by vaccines," he said in a Twitter post on Saturday.

"Travel restrictions or border closures are not very useful measures. They affect the economy and well-being of people."

The discovery of the variant has sparked global concern, a wave of bans on travellers from southern Africa and a plunge in financial markets as investors fear the new variant will halt the global recovery from the nearly two-year-old pandemic.

The World Health Organization has classified Omicron - first detected in South Africa - as a variant "of concern" though has cautioned countries not to hastily impose travel curbs, saying they should take a "scientific and risk-based approach".

Since the pandemic began, Mexico has reported more than 3.8 million confirmed cases of COVID-19 and over 293,000 deaths.

Britain, Germany and Italy detected cases of Omicron on Saturday and British Prime Minister Boris Johnson announced new steps to contain the virus, while more nations imposed restrictions on travel from southern Africa and, in Israel's case, barred the entry of all foreigners.