Senior medical leaders have urged David Cameron to step in "at the 11th hour" to break the stalemate between junior doctors and the Government over a new contract.
Hospitals across England are finalising plans for dealing with the first all-out strike by junior doctors in the history of the NHS. It will run from 8am to 5pm on Tuesday and Wednesday.
The British Medical Association (BMA) has defended the walkout, repeating its stance that it will call off the strike if Health Secretary Jeremy Hunt agrees to lift his threat to impose the contract.
Mr Hunt has rejected this offer but wrote to the head of the BMA, Dr Mark Porter, over the weekend calling for an urgent meeting on Monday to discuss some parts of the deal.
The impasse means it looks increasingly likely the strike will go ahead, with thousands of junior doctors withdrawing full labour, including emergency care.
More than a dozen presidents of royal colleges and faculties have written to the Prime Minister on Monday calling for him to end the dispute.
Signatories include Professor Neena Modi, president of the Royal College of Paediatrics and Child Health, Professor Jane Dacre, president of the Royal College of Physicians London, Dr David Richmond, president of the Royal College of Obstetricians and Gynaecologists and Dr Anna Batchelor, dean of the Faculty of Intensive Care Medicine.
The letter said: "You have spoken many times about your commitment to the NHS. In our view, as leaders of the medical profession, the ongoing impasse in the dispute between Government and junior doctors poses a significant threat to our whole healthcare system by demoralising a group of staff on whom the future of the NHS depends.
"At this 11th hour, we call upon you to intervene, bring both parties back to the negotiating table, end this damaging stand-off, and initiate an honest debate about the serious difficulties facing UK health services."
Katherine Murphy, chief executive of the Patients Association, also pleaded for an end to the dispute.
She said: "Both sides seem to be digging in their heels. On behalf of the patients of this country, we plead with the Government and the BMA at this late stage to talk and reach an amicable solution. They must now put aside their past stances and get together round the table to find a way forward in order to end the uncertainty that patients are facing.
"An agreement must be found to prevent still further disruption for patients and raise the morale of hard-working junior doctors. We remain unconvinced about the imposition of a contract. We don't feel such action is helpful in resolving this ongoing dispute."
Dr Porter told BBC Radio 4's Today programme that senior doctors were stepping in to provide emergency care. He also said the Government had "distorted" statistics, which Mr Hunt says shows patients are more likely to die if they are admitted to hospitals at weekends.
A key issue in the dispute is around weekend pay. The new, imposed contract cuts the pay offered to doctors at weekends but increases basic pay.
Asked if he would walk out, Dr Porter said: "I would look at a Government that has distorted the research and statistics to buttress its non-existent case on this, I would look at a Government that has refused to listen to royal college advice and indeed ignored public opinion on this and I would look around and see the senior doctors who are my colleagues in providing safe care. Of course I would."
Responding to Mr Hunt's "lives at risk" claim, he said: "The Health Secretary is trying to find some way to throw mud at the junior doctors of this country who have been providing weekend and night emergency cover since the NHS started."
Dr Porter added: "The reality is we have advised our members to take part in contingency planning and the NHS has put in place a magnificent effort of contingency planning to make sure that safe emergency care will be delivered on Tuesday and Wednesday. It will be delivered by consultants and staff and associate specialty doctors.
"If the Government will call off the imposition, we will call off the strikes. By contrast, the Government has said over the weekend that there is nothing that will get it to call off the imposition."
During the walkouts, junior doctors will refuse to work in emergency care, including A&E, maternity services, emergency surgery and intensive care.
Clare Marx, president of the Royal College of Surgeons (RCS), told the Today programme the dispute was now a "lose-lose" situation.
She added: "We are in uncharted territory so it is difficult to know what is going to happen."
On Saturday, a coalition of MPs including Labour shadow health secretary Heidi Alexander urged Mr Hunt to test the new work contract in a small number of trusts rather than impose it across England without the support of the BMA.
However, the Health Secretary insisted that the Government was already planning to roll out the contract slowly and dismissed the proposal as Labour "opportunism".