Around 12 million children under the age of five are hospitalised with chest infections such as pneumonia and bronchiolitis each year, a global study suggests.

Researchers also found that an estimated 265,000 children under five suffering from chest infections die in hospital each year.

Almost all of these deaths - 99 per cent - take place in the developing world. About eight out of ten children who die from chest infections do so outside of hospital care.

Researchers at the University of Edinburgh, who carried out the study based on 2010 data, say that the findings indicate the severity of the problem in developing nations. They also suggest that alternative strategies should be explored in order to deal with the impact of the diseases.

The study found that a substantial number of children under five who became critically ill from chest infections were not treated in hospitals. Around 38 per cent of severe cases did not reach hospitals.

Researchers also discovered that boys were more likely to be hospitalised because of chest infections than girls, both because male children are slightly more susceptible to chest infections and because families are more likely to ensure they receive health care than female children. This gender disparity was most pronounced in South Asia.

The study - the first of its kind - is published in The Lancet and supported by the World Health Organization. Its results were produced by a large international consortium of 76 researchers from 39 institutions, in 24 countries.

Dr Harish Nair, of the University of Edinburgh's Centre for Population Health Sciences, who led the study, said: "Pneumonia has an enormous impact upon the lives of young children across the world. This study shows that much more could be done to reduce infection and save lives, such as by improving access to hospitals in the developing world, or by ensuring that both boys and girls receive similar health care."

Researchers from around the world produced the estimates by using hospital-based studies of chest infection rates and data on health-care seeking in developing countries.

The study builds on previous research, also published in the Lancet in 2010 and 2011, which found that around 34 million children develop human respiratory syncytial virus (RSV)-related pneumonia and 20 million children under five develop seasonal flu-related pneumonia each year.