CROYDON University Hospital declared a 'major internal incident' this morning due to unprecedented demand on its A&E department.
As of 7am on Tuesday the hospital put in place a series of emergency measures to cope with the pressure.
It has asked people to only come to A&E if they have a "genuine emergency".
The trust said this afternoon that major incident procedures had since been "stepped-down".
The London Road hospital is the latest in England to declare a major incident as staff struggle to cope with patient numbers.
Hospitals in Surrey, Staffordshire, Gloucestershire and Cheltenham have also implemented the emergency measures.
Croydon did not turn away ambulances or cancel outpatient appointments, steps taken by other hospitals, but five routine operations were postponed and will be rescheduled "as soon as possible".
Declaring a major incident means hospitals can bring in extra resources in such as specialist teams, additional staff and equipment.
It is defined as an emergency that cannot be managed with routine arrangements.
There are currently no other major incidents declared in London hospitals.
A Croydon Health Services spokesman said: "Like a number of hospitals, we are currently seeing a very high number of people in our A&E, many of whom require admission into hospital.
"To increase our capacity we have put in place a series of actions to help meet this increased demand.
"We plan for a busy winter every year and we have taken this step to make sure we can continue to care for people quickly and safely."
The spokesman added: "At no point have we turned away blue-light ambulances.
"We have many more staff than we had two years ago - including 100 extra nurses - but our staff are stretched.
"We are bringing in doctors and nurses together in the right places to care for patients and open up more hospital beds."
The spokesman said additional consultants had been brought in to triage patients in A&E to "get people the right care in the shortest time possible".
"We are also working very closely with health services across Croydon to ensure there is ongoing care and support available for our patients in the community or at home where appropriate.
"We would urge everyone to only come to A&E or call 999 if you have a genuine emergency. This will help us to care for people with the most urgent health needs first."
Labour's Croydon North MP Steve Reed said the hospital's problems were an example of the "crisis" facing the NHS under Prime Minister David Cameron.
"Today's news confirms exactly what local people have been telling me for weeks," he explained.
"Croydon University Hospital is one of London's busiest A&E departments, but they're now so overwhelmed by surging demand they can't admit any more patients.
"Only this morning a local woman in her 80s called my office to say that she had waited 12 hours on a trolley bed in a hospital corridor on Saturday night because the A&E was too busy to treat her.
"The Government has created an A&E crisis across Britain and, tragically, it's now hit our local hospital.
"Similar incidents across the country today show the NHS won't survive another five years of this Government."
Croydon Central MP Gavin Barwell said: "The situation at the hospital is clearly a concern.
"Given the rising and increasingly elderly population, there's real pressure on the system. I don't think anyone would deny that.
"There is some good news which should help in terms of Croydon's specific issues. Croydon CCG is going to get a big above inflation increase compared to most parts of the country.
"The CCG hasn't said how it's going to use that money but you would hope they are going to use it to help the hospital or reduce some of the demand on A&E.
"Croydon clearly also requires a new A&E to help it cope. The current department is way too small for the number of patients it is dealing with.
"It's one of the main things I am working on at the moment and I hope we're going to get some good news on that this year."
Figures published by the Department of Health today show Croydon was in the bottom fifty hospitals for A&E waiting times between October and December, with 87.6 per cent of priority patients seen within the four hour target.
Waiting time performance across England has dropped to its lowest point in a decade.
In December the Advertiser reported that the trust had tried to meet its staffing shortage by hiring 38 nurses from Italy.
It has also drawn up plans for a new £17.5 million revamp of its current A&E department.
