A&E units across the country were braced on Thursday for an “immediate surge” in patients after the ambulance strike, an NHS chief said.
Saffron Cordery, interim chief executive of NHS Providers, told Times Radio: “I think what we will see over the coming days is some of that pent-up demand, people who did not access services yesteday, coming forward.
“So, we are going to potentially see an immediate surge of patients coming into A&E departments, for example.
“In terms of the overall impact, that is going to be incredibly hard to assess.”
Paramedics and 999 call handlers walked out for a 12-hour ambulance strike from 11am on Wednesday in London, with similar industrial action across most of the country.
Health Secretary Steve Barclay was holding talks on Thursday with junior doctors’ leaders in an attempt to avert a 72-hour walk-out in March.
He has highlighted how health workers including nurses and paramedics are pressing for a pay boost for the “here and now” rather than just from April.
So far the Government has declined to offer a one-off payment or backdating the 2023/24 pay rise to the start of this calendar year.
Health unions are now threatening more strikes and to not engage in the public pay body process to agree the 2023/24 wage increase.
Ms Cordery said the fallout from industrial action "diverts attention away from the things the NHS is absolutely keen to focus on", such as cutting waiting times and getting community services back on track.
She stressed that other services, including community services, would have had to step forward to help with calls on Wednesday, leaving "gaps" in care elsewhere.
"That's not to indicate that we think ambulance services, that we think nurses shouldn't strike - it's just to talk about the impact of those strikes," she said.
"We really hope they (unions and Government) can have a constructive conversation and avert some industrial action.
"It would be great if the Secretary of State would come to the table and talk about pay because hopefully then that would set the pattern for ... paramedics, for ambulance staff, for nurses."
Former NHS chief Lord Crisp said Rishi Sunak and other ministers needed to recognise the health service was in “crisis” as they seek to tackle waiting lists of more than seven million, workforce shortages and challenges including caring for an ageing population and the “twindemic” of Covid and flu.
It comes as data released on Thursday showed the number of patients waiting more than 12 hours to be admitted to A&E in London hospitals had risen by a third in a month.
A total of 1,009,995 people were awaiting routine treatment in the capital at the end of October, according NHS figures.
More than 30,000 people were waiting longer than 52 weeks, the figures showed, while 2,025 were waiting longer than 78 weeks.
This is a 139 per cent in a decade. In October 2012, 421,802 Londoners were on the waiting list.
Mayor of London, Sadiq Khan, said: “The NHS in London is in crisis due to chronic underfunding and consistent mismanagement by the Tory government.
“The length of the NHS waiting list in our city has also more than doubled over the last decade. This is simply unacceptable. Londoners are being denied their right to access the treatment they need through the NHS because of the failings of this government.”