Taïna Cenatus, a 29-year-old culinary student in Haiti, lost her balance at school one day this month and toppled over, but it was not until she hit the ground that she realized she had been hit in the face by a stray bullet.

It left a small hole in her cheek, just missing her jawbone and teeth.

Unlike many Haitians wounded by gunfire in the middle of a vicious gang takeover of the capital, Port-au-Prince, Ms. Cenatus was actually lucky that day — she made it to a clinic. But she is still in pain, her wound swelling, and she cannot get any relief, with more and more hospitals and clinics abandoned by staff or looted by gangs.

“My teeth hurt,” she said. “I can feel something is wrong.”

A gang assault on Haiti’s capital has left an already weak health care system in tatters.

More than half of the medical facilities in Port-au-Prince and a large rural region called Artibonite are closed or not operating at full capacity, experts said, because they are too dangerous to reach or their medicine and other supplies have been stolen.

In a country where the United Nations estimates that up to one million people are facing the threat of famine, the unraveling of the medical infrastructure threatens to put thousands more lives at risk.

Even in periods of less upheaval, the public health system was already in shambles, but now hospitals run by humanitarian groups and churches that many Haitians depend on are closing one by one.