Theresa May has slammed the Red Cross description of a "humanitarian crisis" in the NHS as "irresponsible" and "overblown".
In angry exchanges during Prime Minister's Questions, Jeremy Corbyn had accused the Prime Minister of being "in denial" over the extent of the challenge facing the health service.
He said she had ignored doctors, who have warned "patients' lives are being put at risk".
Mrs May hit back at the charity over its criticism as the Government faces intensifying pressure to take action to tackle the problems facing the health service.
:: Nurse in tears over lack of bed for 99-year-old
She said: "... we've all seen humanitarian crises from around the world and to use that description of a National Health Service, which last year saw two-and-a-half million more people treated in A&E; than six years ago was irresponsible and overblown."
The Labour leader had earlier confronted Mrs May with the story of a 22-month-old boy, who was treated on two chairs pushed together and covered by a blanket because there were not enough beds.
Mrs May replied: "I accept there have been a small number of incidents where unacceptable practices have taken place.
"We don't want those things to happen, but what matters is that the NHS looks into issues where there are unacceptable incidents that have taken place and then learns lessons from them."
Earlier, Mr Corbyn had challenged her over the 485 patients forced to wait more than 12 hours on trolleys in hospital corridors last week - three times more than in the whole of January last year.
The Prime Minister has held the line that it is "not unusual" for there to be pressures on the NHS over winter and the Government had provided £10bn extra funding for the health service, a figure which has been widely disputed.
Speaking to the Public Accounts Committee on Wednesday afternoon, Chief Executive of NHS England Simon Stevens said the money was over six years and the NHS had not got what it asked for.
Mr Stevens said that in real terms NHS spending per person in 2018/19 would go down and added: "It does not help anybody to pretend there aren't finance gaps."
Labour's shadow health secretary, Jonathan Ashworth, said the PM had "buried her head in the sand" and that Mr Stevens' evidence had "blown out of the water" her argument over NHS finances.
He said: "Enough is enough. Theresa May needs to come out of her bunker, admit she's got it wrong and guarantee the funding the NHS needs."
(c) Sky News 2017: Theresa May blasts Red Cross as 'irresponsible' on NHS