A man was slashed across the face with a box cutter while aboard a subway train in midtown Manhattan on Thursday morning, and he tried to chase his attacker all the way up to the sidewalk, shocking witnesses, authorities said.

The NYPD said that the victim and another man were arguing on a northbound D train when the man attacked him around 10:15 a.m.

The 38-year-old victim chased his attacker from the platform upstairs to the sidewalk, police said.

Photos from the scene showed a bloodied victim standing in the subway as it stalled at 42nd Street, a shocked look on his face.

Brian W.

"He was standing there and there was blood all over his shirt," said witness Irene Malinoski.

The attacker disappeared. The victim was taken to Bellevue hospital in stable condition.

NYPD Assistant Transit Chief Vincent Coogan said witnesses told police they couldn't tell what they were arguing about. Police say they don't believe the two knew each other but may have both boarded the train at West 4th Street.

Police later released a surveillance photo of the suspect, who's still being sought.

NYPD

B and D trains were re-routed over the C line between West Fourth Street and Columbus Circle while police investigated the scene. Police have recovered the box cutter.

Slashings and stabbings on the subway show attacks are keeping pace with last year, about 52 to date in 2016, compared to 53 for the same period last year. They were a more pronounced concern earlier this year in the late winter months, when they were up about 20 percent in March. The NYPD rolled out the "Cutting Edge" operation in response.

Anyone with information on the slashing should call Crime Stoppers at 1-800-577-TIPS.