Boris Johnson has warned “we have a really tough fight on our hands” as coronavirus puts immense pressures on the NHS, including shortages of oxygen.

The Prime Minister said the nation stands at a “very perilous moment” in the fight against the pandemic, as a hospital in Essex was told to reduce the levels of oxygen being administered during a “critical situation”.

Mr Johnson said that around 2.4 million jabs have now been delivered to around two million people across the UK, with immunity being built up as older individuals are vaccinated.

“But it’s a race against time because we can all see the threat that our NHS faces, the pressure it’s under, the demand in intensive care units, the pressure on ventilated beds, even a shortage of oxygen in some places,” he told reporters during a visit to a vaccination centre in Bristol.

England’s chief medical officer Professor Chris Whitty earlier warned that the next few weeks will be “the worst” of the pandemic for the NHS, with the UK not yet hitting the peak of the current wave of Covid-19 infections.

As NHS leaders warned oxygen supplies were running low in some areas due to Covid-19 treatment, Mid and South Essex NHS Foundation Trust said in a letter to staff at Southend Hospital that the amount of oxygen used to treat patients should be reduced.

“We have reached a critical situation with oxygen supply,” the document, seen by the BBC, said.

“It is imperative we use oxygen safely and efficiently.

“All patients should have a target saturation of 88–92%. Patients with a saturation above 92% which are on oxygen should have their oxygen weaned within the target range.

“I can assure all that maintaining saturations within this target range is safe and no patient will come to harm as a result.”

Yvonne Blucher, the managing director of Southend Hospital, said: “We are experiencing high demand for oxygen because of rising numbers of inpatients with Covid-19 and we are working to manage this.”

Meanwhile, a doctor at a London hospital told the PA news agency that colleagues had been asked to conserve oxygen levels to ensure they did not run out.

Covid-19 case rates in south and east England
(PA Graphics)

“We’ve been told to stagger breaks off of the non-invasive ventilation and make sure we’re aiming for correct O2 targets to conserve (it),” she said.

Chris Hopson, the chief executive of NHS Providers, which represents hospital trusts in England, said there was “huge pressure” on stocks because giving patients extra oxygen was a “key part” of coronavirus treatment.

He told the BBC there were a number of hospitals where this happened in the first phase of coronavirus and over the past few weeks “similar things have happened” elsewhere.

“This is the kind of problem that chief executives and trust leadership teams are having to solve day in, day out,” he said.

“If you (a hospital) push your oxygen to an absolutely critical level, then the thing that you can’t do is have the oxygen system break down… so effectively you will have to dial it down, in which case you will probably have to transfer patients to the nearest neighbouring hospital for a short period of time.

“I cannot tell you how much work has been done over the summer and autumn to ensure that people (hospital trusts) have been prepared for this… they knew they would come under pressure if there were to be further waves, as has now proved to be the case.”