A&E waiting times in England have reached their worst level since records began, data shows.
Figures from NHS England show that, during January, just 84.4% of patients were treated or admitted in four hours, against a 95% target.
This means nearly 330,000 patients waited longer than they should, and comes despite lower levels of flu and norovirus than last year.
The data shows that 83,519 people in January endured very long waits to be admitted to hospital.
After a decision had been taken to admit them, this group waited four hours or more before a ward bed was found for them.
The last time the 95% target - which was introduced in 2004 - was hit was in July 2015.
'Fighting a losing battle'
The data shows that 83,519 people in January waited over four hours to be given a bed after being admitted.
Nuffield Trust chief economist Professor John Appleby said: "Today's figures remind us that the NHS is fighting a losing battle in trying to meet its commitments to provide timely healthcare in the face of the pressure it is under.
"There is a risk that we lose sight of these problems as Brexit distracts us, or become numbed as we forget the last time targets were met.
"But this situation has a serious impact on hundreds of thousands of patients, and will be demoralising for many staff.
"The proportion of patients spending more than four hours in A&E has risen to 15.6% in January - the highest ever in this set of data.
"It looks like the gap between the service's capacity and the care we need from it is widening."
He said only two A&E departments in England met the four-hour target and attendances have risen by an "astonishing 85,000" compared with January last year, at a time in the year when they would usually fall.
Royal College of Emergency Medicine (RCEM) president, Dr Taj Hassan, said: "Sadly the situation afflicting our emergency departments has become seemingly normalised with a 'chronic crisis mode' that does not allow staff to deliver the quality of care they would wish and patients should rightly expect.
"The evidence on resultant crowding in departments is clear - it adds to the risk of harm to patients leading to excess deaths and disability.
"These figures make clear the true scale of this crisis facing our systems."
A spokesman for the NHS said thousands more people have been successfully treated in A&E within four hours than last year.
This is because the total number of attendances has gone up year on year.
He said an average 2,440 more people a day were assessed, treated and discharged or admitted from A&E within four hours in January 2019 compared with the same month in 2018 - an increase of 4.4%.
Miriam Deakin, director of policy and strategy at NHS Providers, said demand for care had put significant strain on trusts and staff but the NHS was treating more patients.
She added: "This is largely down to the work trusts have been doing to improve patient flow and reducing the time patients spend in hospital.
"Improved joined-up working with partners in the community and primary care is also helping to support trusts to manage demand better."