At least one person has died in the United Kingdom after contracting the Omicron coronavirus variant, Prime Minister Boris Johnson said on Monday, the first publicly confirmed death globally from the swiftly spreading strain.

Since the first Omicron cases were detected on Nov. 27 in Britain, Johnson has imposed tougher restrictions and on Sunday cautioned that the variant could overcome the immune defences of those inoculated with two shots of vaccines.

Britain gave no details on the death other than the person had been diagnosed in hospital. It was not clear if the patient had been vaccinated or had underlying health issues.

Deaths from Omicron may have occurred in other countries but none has been publicly confirmed yet outside Britain.

"Sadly at least one patient has now been confirmed to have died with Omicron," Johnson told reporters at a vaccination centre in London.

"So I think the idea that this is somehow a milder version of the virus - I think that's something we need to set (to) one side - and just recognise the sheer pace at which it accelerates through the population."

Health Secretary Sajid Javid said the variant now accounted for 44% of infections in London and would be the dominant strain in the capital within 48 hours. New Omicron infections are estimated at 200,000 per day, Javid said.

Before the death was announced, Britain said 10 people had been hospitalised with Omicron in various parts of England. Their ages ranged from 18 to 85 years and most had received two vaccination doses.

The UK Health Security Agency said Omicron - first detected in South Africa, Botswana and Hong Kong in late November - can overcome the immunity of those who have had two shots of vaccines such as AstraZeneca (AZN.L) or Pfizer-BioNTech (PFE.N).

South Africa's health ministry said it was unable to say with certainty if any of its COVID-19 deaths were caused by Omicron as deaths were not broken down by variant.

The World Health Organization said on Sunday that while preliminary findings from South Africa suggest Omicron may be less severe than the Delta variant - currently dominant worldwide, and all cases reported in the Europe region have been mild or asymptomatic, it remains unclear to what extent Omicron may be inherently less virulent. read more

New lockdowns?

Johnson, now grappling with a rebellion in his party over measures to curb Omicron and an outcry over staff parties at his Downing Street office during last year's lockdowns, said people should rush to get booster vaccines to protect "our freedoms and our way of life".

After COVID-19 was first detected in China in late 2019, he faced criticism for initially resisting lockdown.

He has also been criticised for overseeing mistakes in transferring patients into care homes, and for building a costly test-and-trace system that failed to stop a deadly second wave.

Johnson has repeatedly said that while mistakes were made, the government was making decisions swiftly in the biggest public health crisis for generations and that it was quick to roll out vaccines.

More than 146,000 people have died from COVID-19 in the United Kingdom.

Asked if he could rule out tougher restrictions in England before Christmas, Johnson avoided giving a direct answer. His health minister, Javid, said he knew of no plans for additional measures. "There are no plans that I am aware of for any further restrictions," Javid said.

Vaccine queues

Johnson faces growing anger from libertarians in his party over tougher curbs on daily life and sinking poll ratings.

He has also faced criticism over his handling of a sleaze scandal, the awarding of lucrative COVID contracts, the refurbishment of his Downing Street flat, and a claim that he intervened to ensure pets were evacuated from Kabul during the chaotic Western withdrawal from Afghanistan in August.

An Ipsos MORI poll for The London Evening Standard newspaper showed opposition Labour leader Keir Starmer's ranking was 13 percentage points ahead of Johnson, the first time a Labour chief was viewed as a more capable prime minister since 2008.

It also echoed other polls by showing Labour up three points on 39% ahead of Johnson's Conservatives, who were down one point since the last survey in November on 35%.

At St. Thomas' Hospital Vaccination Centre in central London, a queue of hundreds of people snaked back onto Westminster Bridge. Reuters journalists also documented queues across London and in Manchester, northern England.

"The COVID vaccine booking service is currently facing extremely high demand so is operating a queuing system," the National Health Service said on Twitter. It suggested trying again later.