Britain’s health minister has declined to rule out the chance of further COVID-19 restrictions before Christmas, saying the spread of the Omicron variant is a very fast-moving situation.

The nation has reported a surge in Omicron cases, which government advisers said could be just the tip of the iceberg.

On Saturday, London’s mayor declared a “major incident” to help the city’s hospitals cope.

“We are assessing the situation, it is very fast moving,” Health Minister Sajid Javid told BBC Television when asked whether he could rule out new restrictions before Christmas.

“There are no guarantees in this pandemic. At this point, we just have to keep everything under review.”

Mr Javid said the government was watching the data on an “almost hourly basis” and listening to its scientific advisers. It would balance that against the broader impact of restrictions on things such as businesses and education.

He said there was still much unknown about Omicron but waiting until data was clearer might leave it too late to react to the variant.

Cabinet Office minister Steve Barclay held a meeting of the government’s emergency committee on Sunday (local time) to discuss the situation with Britain’s devolved administrations and agreed to increase their funding to tackle the spread of Omicron.

“They agreed to continue to monitor the emerging data over the coming days, working closely with businesses and public agencies across the UK to understand the impact on industry and services,” a Cabinet Office official said.

More than 100 of Prime Minister Boris Johnson’s own Conservative MPs voted against the government’s latest measures to tackle the spread of COVID last week and Mr Johnson faces the biggest crisis of his premiership after a litany of scandals and missteps.

Asked if Mr Johnson was too weak to bring in further curbs, Mr Javid said, “No … if the government felt that further action had to be taken of course we would present that to parliament and it would be for parliament to decide”.

The most recent number of confirmed Omicron cases recorded across the country was 37,101, the UK Health Security Agency said on Sunday, up by more than 12,000 cases from 24 hours earlier.

Twelve people believed to have had the Omicron variant had died as of Friday.

Mr Javid said the actual number of Omicron infections was likely to be a lot higher.

The number of all COVID cases reported in official data on Sunday was 82,886, up 51.9 per cent over the seven days to December 19 compared with the previous week.

Mr Javid said the government believed about 60 per cent of new COVID-19 cases in England were Omicron.

London Mayor Sadiq Khan said he thought restrictions were inevitable, with the health service under the threat of collapse under the joint pressures of staff shortages and increased hospitalisations.

-AAP