The number of people waiting over a year for hospital treatment in England has hit its highest levels since 2008
Patients are meant to be seen within 18 weeks - but nearly 140,000 of the 4.35 million on the waiting list at the end of September had waited over a year.
Surgeons said it was "tragic" patients were being left in pain while they waited for treatment, including knee and hip operations.
And others warned the situation could become even worse during winter.
Prof John Appleby, director of research at health think tank the Nuffield Trust, said the situation was a "real concern".
Hospitals were facing a real battle to keep non-Covid services going, he said, pointing out the number of Covid patients in hospital had risen from just over 2,000 to more than 10,000 since the end of September.
"It is clear that over the summer months, NHS staff have put in tremendous amounts of work to boost activity across the board," he said.
"However, the service has fallen short of the tall order of recovering all non-Covid activity between the two waves of this pandemic."
Royal College of Surgeons of England president Prof Neil Mortensen said these patients had paid a "heavy price".
"It is tragic to see so many lives put on hold,2 he said.
"Each statistic represents someone waiting patiently, potentially in pain, for the treatment they need to get on with living an independent life.
"Older people and poorer people are particularly hard hit by these delays."
Tracey Loftis, of the charity Versus Arthritis, said the situation was "appalling".
"We're currently seeing some hospitals entirely pausing elective surgery because of the pressures of the second phase of the pandemic," she said.
"The consequences of these further delays will reverberate for years to come."
Chris Hopson, of NHS Providers, which represents hospitals, said the NHS was doing its best but was facing a really challenging winter.
"We are keenly aware of the inconvenience, anxiety and distress for patients caused by any delays for diagnostic tests, treatment or consultations," he added.
Alongside routine care, significant numbers have missed out on treatment for cancer.
The numbers receiving urgent check-ups have dropped by a quarter during the pandemic, with 300,000 fewer people seeing a cancer specialist from April to September than during the same period last year.
The numbers starting cancer treatment are also down by a fifth.