A good Samaritan was stabbed on a Manhattan train early Monday, cops said.

The 27-year-old straphanger was trying to stop a man who had been harassing passengers on a southbound B train at 47th–50th Streets–Rockefeller Center station at 2:20 a.m., authorities said.

Then the man, described as in his 50s, stabbed him in the stomach, cops said.

The victim was taken to Weill Cornell Medical Center with non-life-threatening injuries, police said.

The suspect fled and no arrests had been made hours later.