"Exhausted caregivers = endangered patients", "Public hospitals in life-threatening emergency" were some of the protesters' mottos.
Thousands of French health workers took to the streets of Paris and other cities on Thursday with a rallying cry: "Save public hospitals`".
Protesters say recent spending cuts have harmed care in a country with a health system once the envy of the world.
President Emmanuel Macron promised to respond to demonstrators with "strong decisions" to be announced next week.
"We must (...) take responsibility to invest more strongly than we had planned," Macron said on Thursday, adding that he "heard the anger and indignation" of health workers.
Health spending cuts
As French hospitals were forced to cut €9 billion from their spending since 2005, hundreds of beds were scrapped while stagnant salaries fuelled a flight to the private sector.
The protesters are demanding €3.8 billion in emergency investment in public hospitals — twice as much as set aside in the draft 2020 budget currently before parliament.
They held aloft placards with messages such as: "Exhausted caregivers = endangered patients", "Public hospitals in a life-threatening emergency" and "The hospital is suffocating, let's save it."
Protests began in March when emergency room staff went on strike. They complained of elderly patients being left for hours on trolleys in corridors while waiting for a bed.
Over 260 emergency rooms nationwide are affected by the movement.
On Thursday, staff from other hospital departments joined the protest to demand a cash injection from the state.
Authorities fear that hospital staff could band together with other disgruntled groups such as transport workers or students.
Railway workers are planning mass strike action in December over pension reforms.
Earlier this week, students have demonstrated across France to protest over precarity and living conditions and show solidarity with a destitute young man who set himself on fire.
Protests marking the first anniversary of the "yellow vest" movement are also planned this weekend.
In an attempt to head off another winter of discontent, the government has promised to take action. Yet it seems to have little room for manoeuvre.
Economy Minister Bruno Le Maire warned that "if we spend money on hospitals," the country will need "save it somewhere else".