The first ever all-out strike by doctors in the history of the UK's National Health Service (NHS) began in England on Tuesday, as junior doctors continue to protest against new contracts they say are unsafe and are being forced upon them.

Thousands of junior doctors — a term used for medical practitioners who are working while still going through their years of training — walked out of both routine and emergency care. It is the latest in a series of strikes over working hours and pay but is the first that has affected intensive care and maternity and accident and emergency wards.

The NHS said "military level" contingency planning had been carried out to protect patient safety during the 48-hour strike, including the cancellation of nearly 13,000 operations and more than 100,000 appointments, the redeployment of nurses and more senior doctors into emergency care, and the cancellation of holiday and study leave.

There are more than 55,000 junior doctors in England, around a third of all medical staff. Doctors who belong to the trade union British Medical Association (BMA) have been in a long-running dispute with the government over planned changes to their contracts, which would mean an extension of their standard working hours to include evenings and Saturdays.

At the moment, any hours worked between 7pm and 7am, or at any time over the weekend, are classed as antisocial and are consequently paid more. The contract is being changed to make basic hours (and pay) last from 7am to 10pm, and 7am to 7pm on Saturdays, as part of a government manifesto pledge to create a "seven-day National Health Service."

The Health Secretary Jeremy Hunt has offered an 13.5 percent basic pay rise but the BMA says this is offset by an overall reduction in the pay for antisocial hours, particularly Saturday pay — disputed by the government which says three quarters of doctors will take home a pay rise. While the BMA agrees with the government drive to create a seven-day NHS it says there is a dire shortage of doctors and funding.

A letter sent by the BMA to Hunt over the weekend suggested the new contract be gradually phased in, so its implications could be analyzed at a select few hospitals before being implemented more widely. However, this offer was turned down by the government.

In an interview with BBC Radio 4, BMA chairman Mark Porter accused the government of distorting research and statistics to buttress its non-existing case on this. He said the government had given junior doctors no other choice.

"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," he said.

Porter said they had advised their members to take part in contingency planning and the NHS had put in a "magnificent effort," meaning that senior doctors would deliver the necessary care. Porter also denied that the BMA had refused to talk. "We have said repeatedly and always that we will call off the strike if the government will call off the imposition. By contrast the government has said... that there is nothing that will get it to call off the imposition."

Karen Smith, who had her spinal procedure cancelled for this coming Thursday, told BBC Radio 4 she was "devastated" when she heard it had been put off. "I am desperately disappointed that it hasn't gone ahead but I do support the junior doctors 100 percent," she said.

"We put our lives in their hands... and our families lives as well and [they're a] highly educated group of people and if they all say that this contract that's been imposed on them isn't safe then I believe it isn't safe."

Clare Marx, president of the Royal College of Surgeons, said: "It just shows how sorry a state we are at at the moment, I didn't ever think we'd get to this stage. The current dispute has got to a lose-lose situation," something she said was particularly impacting patients.

Speaking to parliament on Monday afternoon, Health Secretary Jeremy Hunt said he had spent three years trying to solve this issue, holding 75 meetings. Hunt blamed the "difficult" junior doctors committee for the standoff. It was "totally inappropriate" to withdraw emergency care, he argued.

"We could have had a negotiated solution a long time ago," he said, but claimed the BMA had gone for an "outright win."

"Do you move forward or do you give up?" he continued. "When it comes to patients' safety we're moving forward."

"Where health secretaries have made mistakes in the past is where they have been too willing to compromise on patients' safety."

A poll carried out for the BBC by Ipsos MORI found that public support for the junior doctors is increasing, with around 57 percent backing them against the government.