It will take five years for some hospitals to catch up with the backlog of patient care caused by the coronavirus pandemic, NHS Providers has warned.
The trusts in England worst impacted by the crisis are between three and five years away from returning to pre-COVID levels, according to the association, which represents NHS trusts.
It also claims that COVID-19 has resulted in the biggest backlog of care in England for 20 years – and says it is a "very significant problem" that hospital trusts are still assessing the extent of.
The most recent data from NHS England showed that 4.7 million people were waiting to start treatment at the end of February, which is the highest figure since records began in 2007.
Almost 400,000 patients had been waiting more than a year to start cancer treatment then as well – the highest monthly figure since December 2007.
Delays in care do not just refer to planned surgery and cancer treatment, but also mental health and community services.
Health bosses say they need a "multi-year" plan to address the backlog, with chief executives urging the government to go beyond current targets.
This would include more hospital beds, medical equipment, doctors and nurses as well as vast improvements in diagnostics and trauma care, NHS Providers said.
It also says hospitals need to be completely reconfigured to cope with further potential waves of coronavirus.
"This isn’t just about money – it’s actually about how the NHS is going to need to transform the way it provides care," NHS Providers chief executive Chris Hopson told Sky News.
He also said the full size of the problem is unclear because many patients who might have been referred for treatment over the last 12 months have not been, because of the pandemic.
As the NHS emerges from the COVID crisis, Mr Hopson said there is an "opportunity to do things differently", adding that hospital trusts and the government need to form a plan together.
He said there was a similar situation in the early 2,000s, which was tackled with lots of overtime and the use of the private sector.
But this time there is an added problem because the NHS has to work out how it "lives long term with COVID", Mr Hopson added.
These latest concerns follow a row over medics’ wages, with many claiming they will leave the profession, causing catastrophic staff shortages, if the government doesn’t improve salaries across the board.
Prime Minister Boris Johnson has insisted the government will ensure the NHS has what it needs to tackle waiting lists.
"We do need people to take up their appointments and to get the treatment that they need," he said this week.
"We’re going to make sure that we give the NHS all the funding that it needs, as we have done throughout the pandemic, to beat the backlog."
The Department of Health and Social Care said: "Our NHS has faced significant challenges over the past year and we continue to support our incredible health and care staff who have kept services open this winter for thousands of patients.
"We are backing our NHS with an extra £7bn for health and care services this year, bringing our total additional COVID-19 investment to £92 billion.
"This includes £1bn to support NHS recovery by tackling waiting lists and providing up to one million extra checks, scans and additional operations."