The relatively low number of intensive care beds in UK hospitals means it is poorly prepared for major disasters, a report in the Lancet says.
Critical care experts say there may be as few as 3.5 intensive care beds per 100,000 people in the UK, compared with more than 24 per 100,000 in Germany.
The experts from Canada also said demand for intensive care was likely to rise with an ageing population.
A Department of Health spokesman said the number of beds was rising.
Extra wards 'nice'
Dr Gordon Rubenfeld, from Sunnybrook Health Sciences Centre in Toronto, said that huge investment would be needed to keep pace with the growing demand for intensive care services.
One figure suggests that by 2030, the incidence of acute lung injury will have risen 50%, driven by pneumonia cases in older people.
Dr Rubenfeld analysed the availability of critical care beds in various countries, and while conceding that the figure of 3.5 per 100,000 might under-represent the true position, he concluded that, at present levels, the UK would not be in a good position to deal with the extra demands of a disaster.
He said: "It is clear that the UK is at the low end of ICU bed capacity, and thus would have decreased ability to cope with a large-scale disaster with many critically injured casualties."
Currently, an intensive care bed costs the NHS about £1,500 a day, and Professor Mervyn Singer, from University College London, said it was unrealistic to expect a significant expansion of intensive care at a time when health budgets were shrinking in real terms.
He said: "We are clearly in a worse position than some other countries because there is no spare capacity in the system, with many units running at 100% capacity, or close to it.
"While it would be nice to have extra wards and staff ready in the event of a disaster, it is not a particularly pragmatic expectation.
"There are things you can do in the event of a disaster, such as cancelling surgery, which frees up beds, but it is very much a 'make do and mend' approach in these circumstances."
Dr Kevin Gunning, a consultant in intensive care at Addenbrooke's Hospital, Cambridge, and a spokesman for the Intensive Care Society, said that in the event of a major pandemic or other disaster, the true determinant of intensive care capacity would be staff such as trained nurses rather than beds or equipment.
While there had been significant improvements since the year 2000, when a severe outbreak of winter flu caused problems across the NHS, he said the UK was still relatively poorly resourced compared with much of western Europe.
He said: "It's fair to say that we would have struggled with a flu pandemic of the scale some were predicting last year.
"If we have a pandemic of normal winter flu we would be stretched to the limit."
A Department of Health spokesman said: "The number of beds has increased and continues to increase but more does need to be done in some areas.
"However, international comparisons are difficult because there is no internationally agreed or clearly accepted definition of a 'critical care bed' or in the way that services are configured and delivered.
"It is for local healthcare commissioners and providers to assess the number of critical care beds needed locally to meet the demands of their population."