The number of patients waiting longer than six months to start planned NHS hospital treatment has now exceeded 200,000, figures show.
NHS England referral to treatment (RTT) statistics for May reveal that 211,324 patients waited more than six months to start planned treatment.
This is 48.4% higher than the same time last year.
The Royal College of Surgeons said six months is too long to be waiting for treatment for many patients, with some likely to be in severe pain and discomfort.
It added that the total waiting list size is now estimated to be 4.3 million, and warned that hospitals must get their waiting lists under control before the beginning of winter when the situation could become even worse than the last.
The figures also show that Accident and Emergency departments faced their second busiest month ever in June.
There were 2,091,318 A&E attendances last month, while the highest ever was in May at 2,161,779 attendances.
Other RTT statistics reveal that the Government's target of 92% of patients being seen within 18 weeks remained unmet for the 27th consecutive month, having not been met since February 2016.
The figures show that 88.1% of patients were seen within 18 weeks, compared with 90.4% during the same period last year.
The number of patients waiting longer than 18 weeks for planned treatment in May was 485,201.
Susan Hill, senior vice president of the Royal College of Surgeons and a vascular surgeon, said: "Six months will be too long to be waiting for treatment for some patients.
"It is extremely stressful for patients and their families to have to wait this long. These patients will be in severe pain and discomfort, possibly unable to work or carry out daily tasks.
"Not enough has been said about how the NHS plans to deal with the backlog of patients that built up over last winter. Hospitals must get their waiting lists under control before the next winter creeps up and we find ourselves in an even worse position.
"The NHS has been promised a very welcome birthday cash injection, which we hope will help hospitals begin to chip away at these very long waiting times.
"Meeting planned surgery targets must be prioritised in the NHS's forthcoming 10-year plan."
June's A&E performance for the proportion of patients seen within four hours was 90.7%, exactly the same as this time last year, despite the fact that this June was busier.
There was also continued improvement of performance for delayed transfers of care at 139,204 delays - the lowest since April 2015.
Executive medical director and chief operating officer of NHS Improvement Dr Kathy McLean said: "June was the second busiest month A&E has ever faced.
"It is testament to the non-stop work of NHS staff that performance held steady compared to the same time last year, seeing over 80,000 more patients within four hours than in June 2017.
"At the same time, the number of patients facing delays when ready to leave hospital has also reduced to its lowest level since April 2015.
"But there is still considerable ground to make up. Thousands of patients up and down the country are still waiting too long in A&E and for planned surgery."
Janet Davies, chief executive of the Royal College of Nursing, said the figures should leave new Health and Social Care Secretary Matt Hancock "in no doubt as to the scale of the task ahead of him".
"While he is not personally on the hook today, the Health Secretary must look at the slew of bad figures and know that his time in office will be judged against the performance of the NHS," she added.
"A&E admissions are climbing as the temperature soars, and there are neither the staff nor the resources to cope.
"Safe and effective patient care relies on having enough nurses, and the Health Secretary must urgently address the staff shortages that are crippling our healthcare system."
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