United Lincolnshire Hospitals, which runs four sites across the county, said it is having to take "additional steps to maintain services".

In a statement late on Sunday, the trust's medical director Dr Colin Farquharson said: "As a result of significant staffing pressures due to absence related to COVID-19, we are having to take additional steps to maintain services.

Schools urged to merge classes to deal with teacher shortages

"Our staff continue to work exceptionally hard and we would like to reassure our patients and the public that in spite of the challenges faced, essential services remain fully open for anyone who needs them, so people should continue to come forward for care."

Dr Farquharson added that people can help "reduce pressure on health services" by getting their booster jabs.

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In Wales, Swansea's Morriston Hospital said it could provide only a "limited service" in its emergency department over the bank holiday weekend owing to staffing pressures "worsened by COVID".

NHS leaders warned last week that the country faces an intensifying "health emergency" as hospitals struggle to maintain safe staffing levels due to coronavirus sick leave.

Matthew Taylor, who is head of the NHS Confederation, said that if the doubling in hospital admissions seen over the past two or three weeks continues, the stress on the system will build further.

"We would then be in a situation where it would be just very hard for the health service to do anything else than deal with coronavirus," he told Sky News.

Elsewhere, the Department for Education has urged schools to consider merging classes to deal with teacher shortages.

In an open email, minister Nadhim Zahawi asked school leaders to consider "flexible" teaching options so that pupils can still return to the classroom on Tuesday.

It has already been announced that face masks will become mandatory in classes and 7,000 further air purifiers will be delivered to schools to help stop the spread of the virus.

But overall, ministers say there is currently "no evidence" to support more COVID restrictions in England thanks to Plan B measures introduced late in 2021.

The devolved governments in Scotland, Wales and Northern Ireland have all bolstered restrictions in light of the Omicron variant.