Pressure of patient numbers caused a third of the 150 English hospital trusts to warn they needed urgent action to cope last month.
In the worst cases, seven of the 50 trusts that issued alerts announced they were unable to give patients comprehensive care.
Nigel Edwards, chief executive of the Nuffield Trust, which collated the figures for the BBC, warned the situation could deteriorate further in the next two weeks.
He told BBC Radio Four’s Today programme: “Anecdotally what you are hearing from chief executives of trusts is that they are experiencing very, very high levels of pressure in their A&E departments.
“The growth seems to be way above what you might expect from what’s happened from the population.
“People feel that they can’t get to see their GP. The population is getting older and sicker, but I don’t think that’s the entire reason behind it.
“The other big pressure is the ability to discharge patients. If you can’t get patients out of the back of the hospital, home, then obviously, the whole system begins to seize up.
“As we know there are major problems in social care. But also NHS community services. The ability of hospitals to get people out is still really tricky.
“We felt, given the numbers of delayed transfers of care, this number of patients waiting to go elsewhere, the increase in norovirus, the obvious increase in activity that we have seen over the past year, and pressures on the workforce, which are absolutely unremitting, they are reasons to be really quite concerned.
“The real crunch point generally comes in week two or three after the Christmas break.
“I think there are early signs that there is a problem.”
The situation has resulted in operations being cancelled and patients left waiting on trolleys, and The Royal College of Emergency Medicine warned patients in affected hospitals could face delays in receiving pain relief and antibiotics, according to the BBC.
Picture: File photo dated 05/04/13 of Leeds General Infirmary. (Lynne Cameron/PA).