NHS Lothian has admitted it does not "have the abilities" to meet demand in the coming months and will reopen two wards at the Royal Victoria Hospital in Edinburgh, which shut its doors in August.
Health chiefs said the extra capacity was required to provide a "safe service" and further wards could be opened if demand increased as winter progressed.
It comes the day after warnings that Scotland could be facing a surge in the number of cases of winter vomiting bug – or norovirus – with a spate of hospital ward closures last week due to the infection.
Chief medical officer Sir Harry Burns warned the "season" for the winter vomiting bug had arrived five weeks earlier than last year.
In a statement, NHS Lothian said the Royal Infirmary of Edinburgh – which opened at a new £150 million facility in 2003 – was facing increasing pressure from emergency admissions. Among the factors being blamed for the problem is the rising population in the area.
It added the situation is being exacerbated by issues such as the winter vomiting bug and numbers of "bed-blocking" patients, who are well enough to be discharged but are awaiting a nursing home place.
Melanie Hornett, nurse director at NHS Lothian, said: "We have taken a long, hard look at the facilities and resources we have available as part of our winter planning exercises and we know we don't have the abilities to meet demand.
"As a result, we have put this temporary solution in place to allow us to serve patients in a timely manner, while increasing our capacity from within."
The statement said plans were in place to increase capacity, but would take "some months" to achieve.
It added: "The contingency plan was drawn up as part of routine winter planning, which in previous years has seen bed numbers increased on other sites, including Astley Ainslie Hospital, Royal Victoria Hospital and Liberton Hospital among others."
The winter capacity issue is the latest in a series of problems which NHS Lothian has faced in recent months.
On Friday, it was revealed the health board – together with NHS Fife and NHS Borders – is facing a shortage in paediatric trainee doctors. During the summer, the children's ward at St John's Hospital in Livingston was closed due to staff shortages.
And earlier this month, NHS Lothian announced it was recruiting around 250 new theatre staff in an effort to tackle a backlog in operation waiting times.
Last year it was embroiled in a waiting times scandal after officials were caught wrongly listing patients as "unavailable" in an attempt to artificially reduce the numbers failing to meet waiting time guarantees.
Labour health spokeswoman Jackie Baillie said NHS Lothian had to address "fundamental weaknesses and management failings".
She added: "To have to reopen a closed hospital due to seasonal demand shows how little planning has been undertaken. There are, yet again, serious questions to be asked about those managers at the top who seem unable to get a grip of the NHS in Lothian."
In April, a Scottish Government report found that the norovirus – which is highly contagious and can cause serious symptoms in young children and the elderly – had been responsible for more than 1000 ward closures in the past four years.
Yesterday, other health boards said they had no serious problems in coping with the winter vomiting bug.
A spokeswoman for NHS Fife said: "We don't have any wards closed with norovirus and it is not an issue from our point of view.
"We would have contingency in place anyway if we do get any wards which have to shut in the future."
A spokeswoman for NHS Greater Glasgow and Clyde said: "We have the capacity as part of our winter planning to utilise a number of additional ward areas should the forecast of an increase in norovirus cases affect our hospitals."