National medical director Professor Sir Stephen Powis believes the service is struggling as 2024 starts with six days of walkouts by junior doctors in England.
They will impact almost all routine care with consultants covering as the NHS prioritises urgent and emergency cases.
Sir Stephen said: “January could be one of the most difficult starts to the year the NHS has ever faced.
“Six consecutive days of industrial action comes at one of our busiest periods.
“The action will not only have an enormous impact on planned care, but comes on top of seasonal pressures such as Covid, flu, and staff absences due to sickness.
“Extensive preparations are in place, but there’s no doubt they are starting 2024 on the back foot.
“Not only will action impact next week, it will continue to have a serious impact for weeks after as we recover services and deal with additional demand.”
Junior doctors will walk out from 7am tomorrow until 7am on Tuesday.
The strike amounts to 144 consecutive hours of industrial action – the longest in the 75-year history of the health service.
The British Medical Association wants junior doctors to get a 35% pay rise, which it says would restore their real earnings to 2008 levels, but the Government says this is unaffordable.
NHS Confederation chief executive Matthew Taylor told the BBC the action will leave hospitals, GP surgeries and other services “skating on very thin ice”.
He said: “Unfortunately it feels like there is a stand-off which is the Government is refusing to enter negotiations unless the junior doctors call off the strike action.
“But the junior doctors are refusing to call off strike action unless the Government commits to investing more money – and that is a pity.
“These days are going to be very damaging.”
An agreement allows striking junior doctors to be recalled for major incidents and extreme circumstances.
The confederation is urging the BMA to respond quickly to requests for junior doctors to go in.
A Department of Health spokesman said: “NHS staff are prioritizing resources to protect emergency treatment, critical care, neonatal care, maternity and trauma.
“We will prioritize patients who have waited the longest for elective care and cancer surgery.”
