A group of 140 senior doctors have written to David Cameron expressing their alarm over proposals to close and reconfigure accident and emergency units around the country.
In an open letter to the Prime Minister, the health experts said they were yet to see evidence that plans to centralise and downgrade A&E services were beneficial to patients.
The signatories, who include eminent physicians, academics and surgeons, also argued the overhaul could place the lives of some of the most vulnerable members of society at risk.
They said: "We write as doctors to express our alarm about the impact of your policy to centralise and downgrade A&E services. We are not against change. But such change must be driven by genuine improvements in clinical care and service efficiency rather than as part of an indiscriminate cuts policy."
The letter continued: "Not only do many people in some of the country's most deprived areas face longer journeys to hospital, but those in rural areas face longer waiting times for ambulances and crowded A&E departments when they arrive. We have yet to see the evidence that such changes are beneficial for patients.
"In our view, the idea of slashing huge numbers of A&E departments without significantly increasing resources for Ambulance services and hospitals taking up the strain or improving access to GPs will place the lives of some of the most vulnerable members of society at risk."
The lobby of experts, ranging from paediatric surgeons, GPs, neurologists, obstetricians, public health academics, radiologists and psychiatrists, to emergency specialists, said many local people feel they had not been adequately informed of the extent of the reforms.
They urged that no further change takes place without a full independent consultation.
Those supporting the reconfiguration argue larger, centralised centres offer better treatment for certain injuries, such as strokes and neurosurgery.
But many say they will be forced to travel further for emergency treatment if units close to them close.