LONDON, U.K.: As hospitals brace for a sharp rise in flu admissions, doctors in England have launched a five-day walkout, escalating a long-running dispute over pay and working conditions with the government.

Doctors began the strike on December 17, marking the latest in a series of walkouts this year by "resident," or junior, hospital doctors, who say their earnings have been steadily eroded over more than a decade.

The government says it cannot afford further pay increases beyond those already agreed, and Health Secretary Wes Streeting criticised the action as "self-indulgent, irresponsible and dangerous".

The strike adds fresh strain to an already pressured healthcare system. National Health Service England warned last week that hospitals were facing a "worst-case scenario" as cases of a virulent flu strain surged.

"Staff will come together as they always do ... but sadly more patients are likely to feel the impact of this round of strikes than in the previous two," said Meghana Pandit, NHS England's national medical director.

Jack Fletcher of the British Medical Association (BMA), which represents resident doctors, said the dispute centres on both pay and a growing jobs crisis that has left qualified medics unable to secure posts.

"We must value our doctors in this country," he said at a picket line outside St Thomas' Hospital in London.

"We saw more doctors taking the step to leave the profession last year than any in the last decade."

Streeting, however, said the conflict was fundamentally about wages.

"There's just a gap - a vast gap - between BMA expectations and affordability," he told lawmakers.

The BMA is seeking a 29 percent pay increase this year to restore doctors' salaries to 2008 levels in real terms.

After winning last year's election, the Labour government agreed to a 22 percent pay rise for doctors in an effort to end a dispute that began under the previous Conservative administration. But tensions reignited after doctors were awarded a further 5.4 percent rise this year.

Public backing for the strikes remains limited. A YouGov survey conducted on December 12 found that 58 percent of respondents were either somewhat or strongly opposed to the latest action.

NHS England said staffing levels during the strike would be lower than usual, meaning hospitals would prioritise life-saving care and reschedule some appointments.

Flu hospitalisations in England jumped by more than 50 percent in early December, reaching an average of 2,660 patients a day, the highest ever recorded for this time of year. Health leaders say the outbreak has yet to peak.