The further seriously ill patients have to travel by ambulance to reach emergency care, the more likely they are to die, reveals research in Emergency Medicine Journal.
People with respiratory problems seem to be at greatest risk, the study indicates.
The findings have implications for the UK government's proposals to close local emergency care departments in favour of fewer more specialised centres, in a bid to save lives, say the authors.
Local closures will inevitably spell longer ambulance journeys for critically ill patients, they say.
The findings are based on a review of life-threatening (category A) calls to four ambulance services in England, representing urban, rural, mixed, and remote areas, between 1997 and 2001.Only those patients who were unconscious, or not breathing, or who had chest pain were included in the study.