Theresa May has rejected the claim from the British Red Cross that there is a "humanitarian crisis" taking place in the NHS.
The charity said its volunteers had been helping people get discharged from overcrowded A&E units, freeing up beds for other patients.
In saying it had been responding to a "humanitarian crisis" in English NHS hospitals, the British Red Cross used the same language it uses to describe the situation in conflict spots such as Yemen and South Sudan.
But appearing on Sky News' Sophy Ridge on Sunday programme, the prime minister said there was no crisis.
"I don’t accept the description that the Red Cross has made of this," she said.
"Yes, there are huge pressures on the NHS but I think first of all we should thank all those dedicated professionals in the NHS who’ve been working so hard over what is always a difficult period in terms of the number of people using the NHS."
May said NHS funding was at record levels, and ministers were "looking for a long-term solution to what has been a problem that has been ducked by governments over the years".
She continued: "The NHS is facing the pressures of the ageing population, that’s why it’s important that it’s the NHS itself that has produced its five-year plan and is now putting that plan into practice."
Labour leader Jeremy Corbyn has called on May to address MPs in the House of Commons tomorrow on the situation in the NHS.
"The crisis in our NHS is unprecedented," he wrote on Twitter. "People are lying on trolleys in corridors waiting to be seen. Hospitals have had to close their doors, unable to admit patients.
"The health service is at breaking point. But this crisis isn't due to an outbreak of disease. It's a crisis made in Downing St by this government – a crisis we warned them about."
I am demanding that @Theresa_May comes to the Commons on Monday and sets out to the British people how she'll fix h… https://t.co/9KBQwO4PyP
NHS England said hospitals were under more pressure than ever before, but rejected comparisons to international crises.
The British Red Cross's intervention comes after 14 hospital trusts' emergency departments declared they had capacity for only the most life-threatening injuries, and an investigation was launched after two patients died waiting on trolleys in a hospital's corridor.
Some trusts have used Twitter to urge people to come to A&E only in life-threatening situations.
Please only use A&E for serious, life-threatening or dangerous conditions. Call 111 who will direct you to the right service if unwell.
"The British Red Cross is on the front line, responding to the humanitarian crisis in our hospital and ambulance services across the country," British Red Cross chief executive Mike Adamson said.
“We have been called in to support the NHS and help get people home from hospital and free up much-needed beds.
“This means deploying our team of emergency volunteers and even calling on our partner Land Rover to lend vehicles to transport patients and get the system moving."
Adamson called on the government to allocate new funding to invest in social care.
“No one chooses to stay in hospital unless they have to, but we see first-hand what happens when people are sent home without appropriate and adequate care," he said.
“We’ve seen people sent home without clothes, some suffer falls and are not found for days, while others are not washed because there is no carer there to help them. If people don’t receive the care they need and deserve, they will simply end up returning to A&E, and the cycle begins again.”
14 health trusts have warned of overcrowding in their A&E units. We're providing support to staff.… https://t.co/Jw54Qcvvyq
Professor Keith Willett, national director for acute episodes of care at NHS England, acknowledged that demand was at its "highest level ever".
But he told BBC News: "I have great respect for the Red Cross as a caring organisation and we have worked with them over recent winters funding and supporting them with their excellent service at home and ambulance service. But on the international scale of a humanitarian crisis, I do not think the NHS is at that point."
While British Red Cross volunteers have worked with the NHS in recent winters, Labour said its most recent intervention was "just the latest staggering example of how the NHS is now being pushed to breaking point".
"For the Red Cross to brand the situation a ‘humanitarian crisis’ should be a badge of shame for government ministers," said shadow health secretary Jonathan Ashworth.
“The stark reality is the NHS is facing a crisis this winter and in need of urgent help from ministers. It’s time Theresa May urgently faced up to her responsibilities and abandoned her policy of systematically underfunding our NHS.”