A critical incident has been declared at several hospitals in Lincolnshire after the increased spread of Covid-19 caused "extreme and unprecedented" staff shortages.
The United Lincolnshire Hospitals NHS Trust told its sites that it is "unable to maintain safe staffing levels", leading to "compromised care" at the heath care centres it covers.
The trust's warning, revealed in an internal letter leaked to the Sunday Times, came amid a severe spike in hospitalisations across England, with hospitals recording an average coronavirus patient increase of 74% in the week to December 27.
In a statement to ITV News, the trust insisted "essential services remain fully open for anyone who needs them" as it urged people "to come forward for care" if they require it.
ULHT 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.
"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."
The trust runs County Hospital Louth, Lincoln County Hospital, Pilgrim Hospital in Boston, Skegness and District Hospital, and Grantham and District Hospital.
The critical incident was declared as the government drew up contingency plans for huge staff shortages of up to 25% at work places across the UK.
Boris Johnson has asked ministers to develop "robust contingency plans" for the absences, as the government acknowledged the high Covid levels could hit businesses hard.
It comes amid reports that work-from-home guidance in England could be set to roll on for most of January.
Steve Barclay, the Chancellor of the Duchy of Lancaster, is chairing “regular meetings” with ministers to assess how the highly transmissible Omicron variant is affecting workforces and supply chains.
He is also keeping close tabs on the situation in schools ahead of pupils returning for the new term.
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The department said Mr Johnson has charged ministers with working with their respective sectors to test preparations and contingency plans to limit disruption from mounting Covid infections.
It acknowledged that, despite the accelerated booster programme, high Covid levels and the increased transmissibility of the Omicron variant could mean businesses and public services face further disruption in the weeks to come.
The Cabinet Office claimed that, so far, disruption caused by Omicron has been controlled in “most parts of the public sector”.
Health minister Ed Argar has said the government is “doing the responsible and sensible thing” by drawing up contingency plans.
Asked on Times Radio about the advice, he said: “What you’re talking about there is Government doing the responsible and sensible thing of preparing for a range of contingencies, making sure that it considers all possible eventualities, even those that are at the very high end of the scale.”
On whether he thought such absence levels were likely to eventuate, Mr Argar said: “I think we model a range of scenarios up to things we think are highly unlikely, but you still do it because that’s what a responsible government does in preparing for all eventualities.”
A further 137,583 lab-confirmed Covid-19 cases were recorded in England and Wales as of 9am on Sunday, the government said.
The government said a further 73 people had died in England and Wales within 28 days of testing positive for Covid-19.
Separate figures published by the Office for National Statistics show there have now been 174,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.