A third of hospital trusts in England warned they needed urgent action to cope with the pressure of patient numbers last month.
In the worst cases, seven of the 50 trusts that issued alerts announced they were unable to give patients comprehensive care.
Operations being cancelled and patients left waiting on hospital trolleys are some of the consequences of the pressures being felt by the NHS, a source told the BBC.
The situation could deteriorate further over the next two weeks, said Nigel Edwards the chief executive of the Nuffield Trust.
Mr Edwards collated the figures and told the BBC that the increase in patient numbers "seems to be way above what you might expect".
The chief executive said part of the problem was a result of the social care crisis, with patients remaining in hospitals because there are a lack of spaces in specialist care facilities.
"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" said Mr Edwards.
The President of the Royal College of Emergency Medicine told the BBC that hospitals are in an "acute state of distress".
Dr Taj Hassan added: "This is on a background of chronic under-funding, under-staffing, both in health and social care, and really also failures in the wider urgent emergency care system."