The strike started this morning as the doctors prepare legal challenges to the UK government's decision to impose changes to their pay and conditions from later this year.
As was the case during their previous strike actions earlier this year, doctors were providing emergency cover, but 5,000 operations and procedures have been postponed.
"Responsibility for industrial action now lies entirely with the government. They must start listening and resume negotiations on a properly funded junior doctors' contract to protect the future of patient care and the NHS (National Health Service)," said British Medical Association's (BMA) junior doctors' leader Johann Malawana.
"This strike is irresponsible and disproportionate, and with almost 25,000 operations cancelled so far, it is patients who are suffering. If the BMA had agreed to negotiate on Saturday pay, as they promised to do through ACAS in November, we'd have a negotiated agreement by now," a spokesperson said.
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The new wave of strikes, with another 48-hour walkout planned on April 26, involves juniordoctorswithdrawing all but emergency care from hospitals across the UK.
The main sticking point remains payments for working on weekends, referred to as anti-social hours, but the government argues that the current arrangements are outdated and changes are needed to improve standards of medical care at the weekend.
The BMA wants all day Saturday to be paid at 50 per cent above the basic rate but the government is willing to offer extra pay only from 5 PM onwards.
A petition of more than 120,000 signatures backing the junior doctors in the dispute was delivered to the DoH today.
It was accompanied by a rally of junior doctors, other health professionals, members of the fire brigades' union, and other activists on UK government headquarters on Whitehall in London as well as a protest outside the DoH.