Junior doctors’ leaders have said they are prepared to stage yet more strikes after the longest stoppage in NHS history, as health leaders warned that this week’s action alone could cripple the health service until spring. On Wednesday night, at the end of the first of six days of strike action, Prof Sir Stephen Powis, NHS England’s national medical director, said its impact would be felt for “weeks and months” as tens of thousands of appointments and operations were ditched and will have to be rescheduled. A blazing row also broke out on Wednesday night as it emerged that multiple hospitals under severe strain had called on junior doctors to return to work due to patient safety concerns, but almost all the requests had been rejected. The Guardian understands that as many as 20 hospitals had submitted so-called derogation requests to the British Medical Association by 9pm, calling on doctors to return to work. But the BMA said the derogation process was being “undermined” and accused several hospitals of failing to illustrate what steps they had taken to mitigate the need for junior doctors to work. All but one of the requests were rejected, and the final one was being considered by the union. The BMA said such requests should come as a “last resort” and only be used in “unexpected and extreme circumstances unrelated to industrial action”. But NHS England said it had “a robust process in place” for seeking derogations from the BMA and always provided “strong evidence” where hospitals needed support. The 144-hour stoppage – due to end at 7am on 9 January – is the ninth time junior doctors have stopped working since last March and the longest strike to hit the health service since it was founded in 1948. However, after thousands of junior doctors in England began the strike on Wednesday, Vivek Trivedi, a co-chair of the British Medical Association (BMA) junior doctors’ committee, issued a new warning that further strikes were not being ruled out. Trivedi confirmed that junior doctors would be willing to accept the 35% pay rise that they have demanded over “a number of years”, but ministers have repeatedly said 35% is unaffordable. With no end to the dispute in sight, Trivedi said junior doctors might have little choice but to strike again and again in 2024. “If the government stall, or they don’t come to the table, or they make excuses, or they try to push things down the line without any clear reason as to why that is happening … then we will be led by our members. “In the past, when those kinds of actions have been displayed by the government, our members have wanted us to call for further strike action. I hope that we don’t have to go there, but I can’t rule it out.” The prospect of further strike action will alarm NHS leaders. Hospitals reported being “exceptionally busy” on Wednesday. Queen Alexandra hospital in Portsmouth said its A&E department was “full” and declared a critical incident. Bolton NHS foundation trust said it was facing “extreme pressure”, with waiting times in A&E of “up to 11 hours”. On Wednesday evening, a critical incident was also declared across the Nottinghamshire NHS system. Warwick hospital warned that it was under “extreme heightened pressure” and Leeds teaching hospitals NHS trust announced that its hospitals were “under significant pressure”. Health officials in East Sussex, South Tees, Gateshead, Greater Manchester, Berkshire, Rotherham and the Princess Alexandra hospital in Harlow, Essex, also reported being busier than usual. Powis said: “This latest round of strike action will not only have an impact on this week, but will have an ongoing effect on the weeks and months ahead as we struggle to recover services and cope with heavy demand.” Hospital bosses said the next five days would be “incredibly tough”. Some expressed fury that the BMA and the government had failed to reach an agreement for “months and months”. Nick Hulme, the chief executive of East Suffolk and North Essex NHS foundation trust, said “patients are paying the price” as the strikes continued. Trivedi insisted that junior doctors were “not hellbent on strikes” and hoped the government would resume talks swiftly. “The notion that we’re hellbent on calling strikes and all we want to do is call strikes is not what we want. What we want is to negotiate an offer we can put to our members and for our members to accept it.” The industrial action, from 7am on Wednesday 3 January to 7am on Tuesday 9 January, comes at one of the busiest times of the year for the NHS as it faces heightened pressure from winter viruses and a surge in people coming forward who delayed seeking help over Christmas and the new year. The NHS has warned that the strike, which will see as much as half of the medical workforce in England stopping work, could lead to “the most difficult start to the year the NHS has ever faced”. It said emergency and urgent care would be prioritised during the strikes and almost all routine care would be affected. Patients are being urged to come forward to seek care if they need it. The health secretary, Victoria Atkins, said: “January is typically the busiest time of the year for the NHS, and these strikes will have a serious impact on patients across the country. “I urge the BMA junior doctors’ committee to call off their strikes and come back to the negotiating table so we can find a fair and reasonable solution to end the strikes once and for all.”