An ambulance is transporting Zsa Zsa Gabor back to the hospital again after the legendary actress started spitting up blood ... TMZ has learned.


Zsa Zsa's husband Prince Frederic von Anhalt tells TMZ he sounded the alarm moments ago because Zsa Zsa could "hardly breathe" at their Beverly Hills mansion.

Anhalt tells TMZ he's "really worried we may lose her this time."

UPDATE: Crisis averted ... Prince tells us Zsa Zsa was diagnosed with pneumonia and a urinary tract infection.  Docs put her on antibiotics and she'll be heading home.