NHS trusts are £1.2 billion in the red as they face increasing demand for services, new figures show.
At the end of December, NHS providers in England reported a year-to-date deficit of £1,281 billion, which is £365 million worse than the £916 million planned deficit, according to NHS Improvement data.
Meanwhile, providers projected an end-of-year deficit of £931 million, which is £435 million worse than planned, the regulator said.
Its latest quarterly report also shows that A&E departments dealt with record numbers of patients between October and December, 5.6 million people visited A&E over the three-month period, which is a quarter of a million more than the same period last year.
Figures from the regulator also show a high vacancy numbers for NHS staff.
NHS Improvement said that there were 100,000 vacancies across England's 234 acute, ambulance and mental health trusts.
Commenting on the data, Saffron Cordery (pictured), director of policy and strategy at NHS Providers, said: "These figures show how the NHS has been pushed to the limit. Despite working at full stretch with around 100,000 vacancies and a real risk of staff burnout, and despite treating 6% more emergency patients year on year in December, trusts can not close the gap between what they are being asked to deliver and the funding available.
"The figures confirm, once again, three key problems the whole NHS provider sector is facing, increases in demand for treatment continue to significantly outstrip increases in NHS funding; trust savings targets remain too ambitious; and there are serious ongoing workforce shortages.
"There is an increasing feeling amongst frontline trust leaders of 'we cannot carry on like this'. The NHS has shown extraordinary resilience in sustaining performance in the midst of an unprecedented financial squeeze. We have managed to keep the show on the road. But the warning signs are now clear and in plain sight. The time to act is now."
NHS Improvement said that the deficit is still not as high as it was in 2015/16 when it stood at £2.47 billion, officials said that the deficit had been reduced through a series of measures including cutting down on expensive agency staff, efficiency measures and "smarter" procurement.
The regulator said that the majority of the financial decline against plan in the current year comes from a small number of trusts with larger than expected deficits.
Meanwhile it said that NHS providers had maintained A&E performance, with 89.5% of patients being seen within four hours, a similar rate to last year.
NHS Improvement chief executive Ian Dalton said: "Some providers appear to have managed the financial pressures better than others.
"We are working closely with those providers whose financial position has deteriorated seriously to ensure that they grip their problems while delivering the best possible care for their patients."
Janet Davies, chief executive and general secretary of the Royal College of Nursing, said that the figures show the "parlous state of NHS finances" and "official figures on nurse shortages".
The data show that nursing roles account for around a third of the vacancies across the health service.
A Department of Health and Social Care spokesperson said: "Despite the challenging winter months, the NHS has cared for record numbers of patients and fewer NHS trusts are expected to be in deficit at the end of this financial year.
"Whilst the NHS was prioritised in the recent Budget with an extra £2.8billion for the next two years, NHS trusts must now tighten their grip on finances.
"There are currently record numbers of staff working in the NHS and the vast majority of vacancies are filled by bank and agency staff so patient care is not compromised. We are supporting staff to improve work/life balance by working more flexibly and have announced the biggest ever expansion of training places for both doctors and nurses."
Nigel Edwards, chief executive of the Nuffield Trust think tank, said the figures showed a "dangerous shortage of nurses, and a worrying picture for doctors".
He added: "Shortages of nurses damage patient care and make working life harder for those who remain, potentially driving them away too."
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