Since this morning, after eating cat food twice it vomited undigested food twice, then I withheld food, but it went on to vomit watery fluid with a trace of blood.

Based on your description, the cat first vomited undigested food and later vomited watery fluid with blood streaks, which may be caused by indigestion or gastric mucosal bleeding. Generally, withhold food and water for half a day to a day, and during this time give an appropriate amount of pet-specific anti-inflammatory medication and probiotics while observing whether symptoms ease.

If the cat does not improve, take it to a veterinary hospital for further examination and treatment.