The parent of a sick child claimed the NHS was being destroyed as he challenged Boris Johnson during a hospital visit.
The Prime Minister was confronted by the angry parent, who claimed there were not enough doctors and nurses.
In a conversation lasting around two minutes, the man said the situation was “not acceptable”.
Mr Johnson was visiting Whipps Cross University Hospital in north-east London when he was challenged by the parent on a children’s ward.
The parent said the situation was “not acceptable” and told the Prime Minister: “There are not enough people on this ward, there are not enough doctors, there’s not enough nurses, it’s not well organised enough.
“The NHS has been destroyed … and now you come here for a press opportunity.”
Mr Johnson said “there’s no press here” but the parent gestured to cameras filming the confrontation, and said: “What do you mean there’s no press here, who are these people?”
The Prime Minister explained he was “here to find out” about the situation but the man said: “It’s a bit late isn’t it? Years and years and years of the NHS being destroyed.”
A spokesman for the Prime Minister said Mr Johnson was visiting public services to see for himself the reality of the situation.
The spokesman said the man was understandably “very distressed” and the Prime Minister was “not going to hide away from those circumstances when he goes on these visits, and so obviously is keen to talk to people and empathise and see what he can do to help”.
“It’s also a reminder of why exactly he is so keen to make the NHS a priority and make sure it’s getting the funding that it requires,” the spokesman added.
Downing Street said the Prime Minister had spent the past six weeks visiting hospitals “to hear directly from NHS staff and patients – and this is exactly why he is so committed to making sure investment reaches frontline services, so that doctors and nurses have the resources they need and patients receive consistently world-leading care”.
A spokesman added: “This is why we’ve recently invested an additional £1.8 billion into frontline services and are upgrading 20 hospitals across the country.”
Labour said Mr Johnson was being confronted by the effects of Conservative austerity and hit out at his claim there was “no press” at the event.
Tottenham MP David Lammy said: “He just can’t stop lying.”
Shadow health secretary Jonathan Ashworth said: “Boris Johnson simply can’t be honest with people.
“He can make as many phoney announcements on the NHS as he likes but he can’t hide from the truth, or from patients.
“The Tories have plunged the health service into crisis through years of cuts and privatisation and the Prime Minister can’t run from the consequences this has had for patient care.”