Hospital doctors in England began a new 72-hour strike over pay on Wednesday, prompting warnings from health officials of huge disruption to patients and services.
The strike is the latest in the state-funded National Health Service (NHS), which has also seen nurses and other medical staff picket for more pay.
The walk-out by junior doctors -- those below consultant level -- started at 7:00 am (0600 GMT) and is set to last until Saturday.
The British Medical Association's Junior Doctors Committee says medics have seen a 26 percent pay cut in real terms in the last 15 years, as salaries have failed to keep pace with soaring inflation.
They want pay restored to 2008-2009 levels but the government says that would mean an average pay award of about 35 percent this year and is too costly.
Instead, it has offered an extra five percent.
The BMA has warned that while it was open to further talks, it would stage further strikes in the coming months if the government sticks to its offer.
At a picket line outside University College Hospital in London, 27-year-old trainee anaesthetist Arianna Zembryzcka said she was struggling to pay rent.
The government's offer was "frankly disrespectful and disgraceful" and would not cover this year's inflation "let alone years of pay erosion", she said.
On Tuesday, NHS England's national medical director, Stephen Powis, warned that most routine or pre-planned care could be affected.
A similar walk-out in April saw 196,000 hospital appointments and operations rescheduled.
"It (the strike) will have an enormous impact on routine care for patients and on the waiting list, as procedures can take time to rearrange with multiple teams involved," he said.
Priority will be given to emergency, urgent and critical care, he added.
Hospital bosses have called for both sides to give ground, as they battle huge backlogs in treatment exacerbated by the Covid pandemic.
Some seven million people were waiting for treatment in April -- a record -- with nearly three million waiting more than 18 months, according to the BMA.
The length of time for patients waiting for their first appointments and treatment for cancer was also getting worse, it added.
Health Secretary Steve Barclay called the strikes "extremely disappointing" and said it put patients and work to cut waiting lists at risk.
"If the BMA cancels these damaging and disruptive strikes and shows willingness to move significantly from their position, we can resume confidential talks and find a way forward, as we have done with other unions," he added.
Junior doctors in Scotland on Tuesday rejected what the Scottish Government in Edinburgh called its "final" pay offer of a 14.5 percent increase over two years.
BMA Scotland said its members would strike from July 12-15.
Health policy is a devolved matter for the governments in Scotland, Wales and Northern Ireland, with the UK government in London overseeing England.