More than 20 NHS trusts have now declared a critical incident over Covid staffing shortages, No10 suggested today.
The Prime Minister's official spokesman said more than 20 trusts have now reached the alert level where priority services may be under threat.
The figure is higher than 15 hospitals whose details were publicly confirmed earlier today.
Morecambe Bay NHS Trust, Blackpool Teaching Hospitals NHS Foundation Trust, The United Lincolnshire Hospitals NHS Trust, the Great Western Hospitals NHS Foundation Trust, University Hospitals Plymouth NHS Trust and University Hospitals Dorset are among the hospital trusts that have signalled they may be unable to deliver vital care to patients due to staff shortages.
Meanwhile, 17 hospitals in Greater Manchester have paused non-urgent surgery and appointments, although a critical incident has not yet been declared at the sites.
It comes after 15% of Greater Manchester hospital staff fell sick with Covid or had to self-isolate, far higher than the usual staff absence figure of 5% over winter.
Yet the PM’s spokesman stressed critical incidents were "not a good indicator" of the pressures the health service was under.
He said: "I think my understanding on critical incidents, obviously the numbers do vary...
“It’s worth understanding that critical incidents can last, in some certain circumstances, a matter of hours, a morning or afternoon, a day some of them can last longer than that.
"So they're not a good indicator necessarily of how the NHS is performing."
He said: "We know that there are a number of trusts that have reported critical incidents.
"I believe it's more than 20 currently, but that number will fluctuate. But again, those critical incidents can vary in terms of their scale, some can relate to one part of the trust, some can be across the whole trust. So it's not a good indicator, necessarily, of NHS performance at any one time."
Huddersfield Royal Infirmary and Calderdale Royal Hospital have also taken steps to protect staff and patients by banning visitors to both sites.
Chris Hopson, chief executive of NHS Providers, said hospitals are able to get assistance from nearby hospitals and other NHS trusts after declaring critical incidents.
He added: "It is a sensible, planned thing to do to ensure that trust can carry on providing the services that it needs to provide, particularly the critical and essential services."
Prime Minister Boris Johnson today told his Cabinet to stick by the Plan B measures in England - despite admitting parts of the health service will feel "temporarily overwhelmed".
In his Covid winter plan last September, he promised to do “whatever it takes to prevent the NHS from being overwhelmed”.
