More than 1,000 people had to wait more than 12 hours to be admitted after being seen at A&E in January, as waiting times reached record levels.
As the NHS struggled through the peak of winter, there were also more than 81,000 patients who waited longer than four hours to be admitted, according to the figures from health think tank the King's Fund.
The figures, which cover hospitals in England, also showed that patients are waiting longer for routine treatment.
Of those who should have started treatment within 18 weeks following a GP's referral, some 12 % waited longer during the month of December, the highest in nine years.
The number of people waiting more than 52 weeks for treatment increased to 1,750, with the think tank warning there was "very little protection for people who can't be treated within the initial time limit".
Richard Murray, director of policy at The King's Fund, said: "With demand for services likely to remain high, it's very unlikely that meeting these targets will become more achievable.
"The waiting time standards should not be abandoned but the NHS needs to ensure the way they are implemented does not leave patients who are not treated within the time limits facing long waits for treatment."
NHS Providers deputy chief executive Saffron Cordery said the waiting times were "disturbing" and that patients "deserve better".
She added: "NHS trusts and frontline staff are doing all they can to ensure patients receive safe and timely care.
"But as these findings show, it is becoming increasingly difficult to achieve this when demand for treatment is growing so quickly, and funding is so tight.
"It is also disappointing to see so many people waiting longer than 18 weeks for planned routine operations. It feels like we are losing the hard-won gains of the last decade.
"We have reached a watershed moment. We need to see urgent steps towards establishing a long-term funding solution for health and social care."
Niall Dickson, chief executive of the NHS Confederation, which represents organisations across the healthcare sector, said the figures were "simply not acceptable".
He added: We need long-term funding commitments, we need a reformed system that joins up different parts of a fragmented system, and we need politicians to wake up to the reality of what is happening."
More from NHS
A spokesman for NHS England said that during December and January, the service treated 130,000 more patients within the four-hour A&E target than over those same months the previous year.
"What's more, the first ever waiting time targets for mental health treatments have been introduced – and are being met – and new ambulance targets mean 750,000 calls a year that used to go into a queue now will get an immediate response."
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