The proportion of patients seen on time in A&E has hit its lowest level since records began.
Figures for February show 87.8% of patients were admitted, transferred or discharged from England's A&E departments within four hours of arrival - below the 95% target.
There were also problems across other key targets, with high numbers of days lost to so-called "bed-blocking".
This occurs when patients who are medically fit to be discharged are stuck in hospital beds, often because of a lack of social care support in the community.
The latest NHS data shows there were 157,569 days of delayed discharges in February 2016, compared to 134,353 in February 2015.
A snapshot shows there were 5,743 patients delayed at midnight on the last Thursday of February 2016 - the second highest number since monthly data was first collected in August 2010 - the highest was in January.
Other targets were also missed, including calls answered by the 111 phone service, ambulance response times, which have been performing particularly poorly, and one cancer treatment target.
Candace Imison, director of policy at the Nuffield Trust, said: "Today's figures are the very visible symptoms of a system facing both inexorably increasing patient numbers and severe financial strain.
"It's disappointing that for the second month in a row, the proportion of people seen within four hours in A&E in February was the lowest since 2004, with almost 230,000 people having to wait longer than four hours.
"But these delays are hardly surprising when you look at the number of patients who had to be admitted to hospital as emergencies - over 450,000 in February, 38,000 more than a year ago, despite a huge policy push to try and enable these people, many of them frail and elderly, to be treated at home or in the community.
"This pressure on wards was in turn not helped by the number of patients in hospital beds whose medical treatment was finished, but who could not be discharged because there was not enough support available for them in the community.
"Unfortunately we are not going to see any significant improvement in meeting the A&E four hour target until the both the number of patients admitted as emergencies, and the number who cannot be sent home, are reduced as well."
Shadow health secretary Heidi Alexander said: "These figures show an NHS on its knees and in crisis.
"Under David Cameron we're heading back to the bad old days of patients waiting hours on end in overcrowded A&E departments or stuck on trolleys because no beds are available.
"The pressures in hospitals are a direct consequence of decisions this Tory Government has taken. Cuts to social care have left too many older people without the support they need to remain independent at home, and it has got harder and harder to see a GP - leaving many people with no choice but to go to A&E."
Richard Barker, interim national director of commissioning operations and information at NHS England, said A&E was "now seeing the effects of the delayed flu spike which peaked in February and March this year compared with pre-Christmas last winter.
"This was compounded by social care-related delayed hospital discharges which are up by 40% compared with the same month last year."
He added: "Despite these pressures, for the year as a whole more than nine out of 10 patients have been admitted, treated or discharged in under four hours, while long trolley waits have halved compared with last year."
The data showed that, of calls answered by NHS 111, 79.7% were answered within 60 seconds against a 95% target, down on the 82.2% reported in the previous month.
On cancer, the 62-day wait for treatment from GP referral was missed (81% compared with the target of 85%). The other key cancer targets were met.
Ambulances missed their target to answer 75% of the most serious 999 calls in eight minutes - the ninth month in a row this has not been achieved.
Slightly less serious calls were also not responded to in time and have not been for two years,
Dr Jennifer Dixon, chief executive of the Health Foundation, said: "The root cause of deteriorating performance is an unprecedented slowdown in funding for the NHS - now half-way through the most austere decade of funding growth since records began in 1948 - and severe cuts to social care, impacting specifically older people.
"Providers are struggling to accommodate this slowdown because of the sheer pace and scale of changes required. Today's performance figures, while worrying, are entirely predictable."
Vicky McDermott, chairwoman of the Care and Support Alliance, said: "The NHS is picking up the bill because the Government is ignoring the crisis in care - a third of all delays are now caused by a lack of social care.
"Delayed discharge alone costs the NHS £900 million a year but inadequate social care isn't just preventing people leaving hospital, it is also driving people to A&E."