The prime minister has blamed COVID-19 for hospital bed shortages and record A&E and ambulance delays plaguing the NHS.
Rishi Sunak insisted that improvements are being made to the health service already but that it is a "reality" that the pandemic contributed to a huge backlog in the system.
"I think it's not right to ignore the impact that COVID had. The reality is that for two years the NHS had to stop doing lots of things that it normally does," he told the BBC's Sunday With Laura Kuenssberg show.
"Unsurprisingly, once we get back to normal, all of those treatments come back at a pace that was anticipated but is obviously very significant.
"Has the NHS had pressures before? Of course it has, but COVID has undeniably had an enormous difference, and it is wrong to ignore that.
"I can't help that COVID happened, I can't help that there are now thousands of people in hospitals who normally would not be there."
Watch: Rishi Sunak refuses to answer whether he uses a private GP three times
The PM said a difference was already being made, with more people who don't need to be in hospital being moved to social care or home.
He said more treatment was being provided outside of hospital to people who've had falls, meaning they don't take up hospital bed space, and that ambulance services are learning "best practice" from trusts that have slashed delays.
However, many health workers on the ground don't feel like the situation is improving much, with the number of free NHS hospital beds sinking to their lowest level ever recorded.
Critics of the government say that problems faced by the health service were mounting long before COVID-19.
As Kuenssberg pointed out to the prime minister, the four-hour target set for being admitted by and discharged from A&E hasn't been met since 2015.
Pressed on whether he accepted that the NHS was under crisis, Sunak said: "Well, as I said, the NHS is under pressure."
He added that "what matters more than words is action", pointing out that three weeks after he became prime minister, his autumn statement included "billions of extra pounds for the NHS and social care".
Sunak said change is already happening but that the problems facing the NHS are "not going to be solved overnight" and that, while delays in A&Es and long lines of ambulances waiting outside hospitals are "unacceptable", around 10% of NHS trusts "account for over half of all ambulance handover delays".
The PM said that following talks with health leaders on Saturday, he had a "renewed sense of confidence and optimism" that the NHS could overcome its hurdles.
However, he refused to say whether his family was registered with a private GP when asked by Kuenssberg, adding: "As a general policy I wouldn't talk about me or my family's healthcare situation.
"It's a distraction from what the real issue is, which is, are we making sure that there's high quality healthcare available for the country?"
Sunak also refused to be drawn on whether he would step-in to help the Royal Family resolve its infighting, following the leaking of details from Prince Harry's highly-anticipated memoir Spare.
The Duke of Sussex makes a number of explosive claims in the book, including that his brother Prince William physically assaulted him, and that his father the King demanded that Meghan Markle be kept away from the Queen as she lay on her deathbed.
There is some precedent for prime ministers getting involved in situations like this, with John Major offering "support and guidance" to Charles and Diana in 1992, before the couple separated.
Sunak, however, said he would "never ever comment on matters to do with the Royal Family".
He added: "I think the public like me have enormous regard for the Royal Family and are deeply proud of them. I certainly am – it's one of the things that I’m most proud of when I think about what it is to be British.
"When I get to go around the world and champion Britain as an amazing country with so many things that we can be proud of, our institutions including the Royal Family are one of those.
"We saw that last year, very movingly multiple times, and I'm confident that we'll see it this year with King Charles's coronation which will be another fantastic occasion for the country to come together and celebrate something special about Britain."