A march highlighting the NHS "crisis" and demanding increased funding has attracted thousands of demonstrators to the streets of central London.
The National Health Service – which is in its 70th anniversary year – has been struggling to cope with what has been described as its worst winter on record.
The march was organised by the People's Assembly and Health Campaigns Together.
They said: "It is time this Government stops blaming patients, nurses, doctors, immigrants, flu and the elderly for their shortcomings."
A respiratory doctor taking part in the protest told Sky News: "The health service is falling apart, and time is running out to sort it out."
Protesters carried placards reading: "Save our NHS"; "More staff. More Beds. More funds"; and "Kick the Tories out".
The protest began in Gower Street and ended in Downing Street.
A Boris Johnson impersonator was also wheeled through the streets on a makeshift hospital bed next to an effigy of Theresa May.
Nurse Danielle Tiplady told Sky News: "Nurses are at breaking point and we've had enough. We are demonstrating because we're demanding that the Government respect us. We want them to restore our bursaries and give us a fair pay rise for the work we do.
"We're also doing it for our patients, because they are really suffering in the NHS crisis. There's a lack of beds, people are being cared for in corridors and patients just aren't getting the care they deserve."
A shortfall of about 40,000 nurses across the UK is adding to pressure on staff at a time when there are more people leaving the NHS than joining it.
A recent health select committee report drew attention to "too few staff on duty", leading to "unacceptable pressure" on nurses who found themselves unable to safely take breaks.
Sky's senior political correspondent Jason Farrell, who was at the march, said: "Desperate language is being used by doctors, and I think that is because over the last month we've seen a real problem.
"The heads of A&E departments have written to Theresa May saying that people have been dying prematurely in corridors because of the lack of beds.
"Currently, the occupancy rate is even worse than it was in the few weeks after Christmas. There are about 40 trusts where it has reached 100% over the last week.
"There has been a spike in the flu, in the norovirus which has been particularly pronounced this year. The number of people being treated has gone up dramatically.
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"There is a continuing row in the Government over the NHS, so this is a political problem for the Conservatives that isn't going away."
NHS England has said it is doing everything it can to deal with the high number of patients.