The Armed Forces have sent 200 personnel into NHS hospitals across London to plug staff shortages.
The Ministry of Defence will provide 40 defence medics and 160 general duty personnel for the next three weeks.
Hospitals in London have been hit hard by staff absences, with thousands off sick or isolating as the Omicron variant surged through the capital.
An additional 32 military co-responders will support paramedics in the South Central Ambulance Service.
Pressure on London hospitals is currently higher than a month ago, with 4,000 patients in hospital with Covid-19 compared to 1,100 in December.
There are 236 patients on ventilators compared with 190 last month and daily admissions are four times higher than in December, with 401 on Thursday, compared with 111 a month ago.
Vaccination rates in the capital are also running behind those in England as a whole, with 69% having had a first dose, 63% a second and 40% a booster jab.
Health Secretary Sajid Javid urged people to get their vaccinations to help cut the pressure on the NHS, as he welcomed support from the military.
He said: “Once again they are stepping up to assist NHS workers who are working round the clock across the capital, helping the health service through this difficult winter period where the need is greatest.
“The most important thing you can do is get boosted now to protect your loved ones and communities from Covid-19.”
Army personnel were also needed in London hospitals during the peak in Covid-related hospital admissions this time last year.
Defence Secretary Ben Wallace said the Armed Forces would again be working “hand-in-hand” with NHS staff “to protect the nation from Covid-19”.
He added: “They have shown their worth time and again throughout this pandemic, whether driving ambulances, administering vaccines or supporting patients in hospital and they should be proud of their contribution to this truly national effort.”
There are 40 teams of five, with one medic and four general duties personnel, who have started work this week and will be allocated according to need.
Medics will work with patients, whereas the soldiers will be working on maintaining stocks, checking in patients on arrival, and conducting basic checks.
Paramedics in the South Central Ambulance Service will also be bolstered with 32 military co-responders, who are expected to stay with them until the end of March.
Jane Clegg, the regional chief nurse for the NHS in London, said: “We are thankful for the support of the armed forces alongside thousands of NHS staff, as they respond to the increased demands brought by Covid – ensuring continued high quality care and treatment for the many Londoners being looked after by the NHS this winter.”
Across the UK there are about 1,800 armed forces personnel supporting the NHS response to the Covid-19 pandemic, made up of regulars and reservists from the Army, Navy and the RAF.
More than 400 military paramedics are assisting ambulance trusts, with 313 in the Welsh Ambulance Service NHS Trust and 96 in the Scottish Ambulance Service.
Another 1,000 are working on the vaccine booster programme, with 730 in England, 221 in Scotland and 98 in Wales.
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