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Speaking to MPs on the Liaison Committee, Boris Johnson said he was "concerned" about the variant, adding: "I think it's fair to say that there are lots of questions we still have."

"We already have tough measures... to protect this country from new infections coming in from abroad," he said.

"We are taking steps to do that in respect of the Brazilian variant."

The prime minister did not announce a ban on travel from the South American country, but instead promised Britain's border controls were enough to stop infections from abroad. 

The new variant in Brazil differs from the ones found in Britain and in South Africa, which have driven a surge in cases.

Britain has already banned direct flights from South Africa to try to limit the spread of the more contagious variant.

During the committee hearing, MP Yvette Cooper questioned the prime minister on why it was still possible to get direct flights to the UK from Brazil.

Mr Johnson responded by saying the government was "taking steps to ensure we don't see the import of the new variant" but didn't elaborate further.

On Sunday, Japan's Health Ministry said it had detected a new coronavirus variant in four travellers who arrived in the country from Brazil's Amazonas state.

Takaji Wakita, head of Japan's National Institute of Infectious Diseases, said there was "no proof" the variant found in Brazil was more transmissible.

Of the four travellers who arrived in Tokyo on 2 January, a man in his forties had a problem breathing, a woman in her thirties had a headache and sore throat and a male in his teens had a fever. A female teenager showed no symptoms, the health ministry said.

Meanwhile, coronavirus variants have raised concerns for the effectiveness of current vaccines.