Health protesters banged drums and sounded air horns as part of a "howl of protest" against planned changes to the NHS.
The group of activists gathered opposite Downing Street in central London to protest against new "sustainability and transformation plans".
The plans aim to show how services in each local region will evolve and become sustainable over the next five years.
David Bailey, an accident and emergency nurse who spoke at the event, warned the plans would mean "the NHS will just end up being a logo on the sign of a Virgin Care facility".
The 54-year-old claimed the plans would mean £22 billion cut from the NHS in England, a figure previously cited by the British Medical Association (BMA).
"This is pretty much a quarter of the budget, and this will mean the beginning of our final battle to save the NHS," he said.
The sustainability and transformation plans (STPs), all of which have been published - and some previously leaked - could see some hospitals, A&E units or maternity units close, and other services merged.
Activists, NHS staff and protesters spoke at Friday's event, which was punctuated by the "howls" of noise.
Around a dozen people then marched down Whitehall to the Houses of Parliament.
Health managers in 44 areas of England have been ordered to draw up the strategies, setting out how they will reduce costs, change services and improve care in the wake of a record £2.45 billion deficit for the last financial year.
Mental health nurse Sami Hillyer said she had seen patients on her ward who had tried to take their own lives.
"The cuts have an impact on people's mental health," she said.
"People are coming in for things that could be avoided if the social security was there to support people."
She said issues such as housing and benefits can impact people's mental health, but that when patients need help they cannot be treated properly.
"We are so short of staff all we are left with is medication," she said.
The 26-year-old said staff can only treat "symptoms but not the causes" of mental health problems.
The sustainability and transformation plans are being drawn up across England.
Sir Bruce Keogh, NHS England medical director, said of the STPs: "I am optimistic they will deliver practical improvements that will really make a difference to people.
"Things like making it easier to see a GP, providing more specialist services in people's homes, speeding up the diagnosis of cancer and offering help faster to people with mental ill health.
"To realise these benefits some communities might need to make choices about where to put resources and the NHS will need to be clear with the public about the options.
"But as communities debate change the overriding concern must be to ensure we can all get excellent care whenever we need it."