Fears that hundreds of thousands of operations and millions of appointments are at risk from new waves of strikes by junior doctors have prompted calls for the industrial action to be reconsidered.

In a joint statement NHS Providers and NHS Confederation have appealed to the British Medical Association (BMA) to cancel the latest walkouts.

Medics will stage strikes from September 12 to 16, on October 5, 6, 7, 10 and 11, November 14 to 18 and December 5 to 9 in the ongoing dispute over a controversial new contract.

The Government and BMA remain at loggerheads over the contract, which the Department for Health says will provide a seven-day NHS.

Chief executive of NHS Providers, Chris Hopson, said the proposed strikes will "lead to an estimated 125,000 lost operations and over one million lost outpatient appointments".

"With barely any notice for trusts to prepare, this unprecedented level of strike action will cause major disruption and risk patient safety," he added.

"NHS trust leaders agree with the Academy of Medical Royal Colleges that this action is disproportionate.

"Less than 40% of junior doctors supported rejection of an agreement strongly endorsed by their own representatives.

"None have voted in favour of four sets of five-day strikes - by far the most disruptive industrial action in NHS history.

"The BMA Council was split down the middle when it considered the proposed strike action.

"Our board and the trusts we represent are therefore formally calling on the BMA to reconsider their proposed strikes for the sake of patients."

NHS Confederation chief executive Stephen Dalton also urged the BMA to reconsider the planned industrial action, saying they "don't think there is a strong mandate for the additional strikes given they go well beyond the initial planned action".

A host of health organisations have also questioned the decision to extend the bitter campaign, which has been called "extremely worrying" and a "devastating blow to patients".

And there have been warnings by one charity that trust in the patient-doctor relationship could be eroded by the months of disruptions.

Reports suggest the latest raft of action was not fully backed by BMA members, with The Daily Mail reporting that a leaked ballot showed just 31.5% of members supported a full walkout which was time-limited.

But the BMA said it was "absolutely behind" the decision for further strikes.

The Patients Association condemned the announcement, saying it was a "disturbing" time to be an NHS patient.

Chief executive Katherine Murphy told the Press Association: "From a patient's point of view it is obviously catastrophic news - the scale of the industrial action is unforgivable.

"It's putting patients under unnecessary stress and worry because every day they're hearing about a crisis in the NHS and the financial problems in our hospitals up and down the country."

She added: "It's a very, very disturbing and worrying time for any patient.

"The public have the greatest sympathy for the medical profession and understand the difficult job that they do, but this may take a step too far and could erode the public confidence and trust."

Nigel Edwards, chief executive of the Nuffield Trust health charity, told the Today Programme that the planned strikes would represent a "quite significant step up" in terms of what is likely to be asked of senior doctors tasked with ensuring that care continues during industrial action.

He added there had been a "quite obvious shift in the opinion" of medical leaders in relation to the strikes.

Six strikes have already taken place across England during the lengthy dispute, causing disruption to hundreds of thousands of patients who have had appointments and operations cancelled.

In May it looked as though a breakthrough had been reached in the dispute after both sides agreed to a new deal.

Then in July, the Government announced that it would impose a new contract after junior doctors and medical students voted to reject the contract brokered between health leaders and the BMA.

The BMA said it will call off the strikes if the Government agrees to stop the imposition.

Dr Ellen McCourt, who chairs the BMA junior doctors' committee, said: "We want to resolve this dispute through talks, but in forcing through a contract that junior doctors have rejected and which they don't believe is good for their patients or themselves, the Government has left them with no other choice."

Newly elected co-leaders of the Green Party, Caroline Lucas and Jonathan Bartley, told the BBC they supported the strike and would take part in picket line protests during the looming dispute.