Thousands of NHS workers, campaigners and union representatives are marching in London to protest “yet more austerity” to the health service.
The protest, called #ourNHS, is marching against plans which could see hospital services in nearly two-thirds of England cut back.
It says pay restraints for NHS staff has led to 25,000 nursing vacancies.
Labour leader Jeremy Corbyn is expected to address protesters at the march, once it gets to Parliament Square.
The march began outside private healthcare company Virgin Care in Tavistock Square, and will end with a series of speeches in Westminster.
The group claims that the government’s proposed Sustainability Transformation Plans (STPs) across the local NHS in England are a “smokescreen for further cuts and are [the] latest instruments of privatisation”.
Last month the BBC revealed that hospital services in nearly two-thirds of England could be cut or scaled back.
The proposals would see the complete closure of some hospitals, and the centralising of some services such as A&E and stroke care, on fewer sites.
On Twitter Dr Ben White said: “#ourNHS sees you from the cradle to grave, with or without insurance. Sadly we must now fight to keep it that way.”
Labour shadow chancellor John McDonnell is one of a number of figures leading the march, which should arrive at Parliament Square at 14:30 GMT.