A man suffered life-threatening injuries when he fell in front of an oncoming subway in Brooklyn Thursday evening, cops said.

The 30-year-old victim was standing on the N-line platform when he fell and was struck by a southbound train just before 5 p.m. at the 59th Street station in Sunset Park, police said. The victim did not fall onto the tracks.

Police said the man suffered a head injury.

He was rushed to NYU Langone Hospital Brooklyn in serious condition, officials said. His condition was later downgraded to critical.

It was not immediately clear what prompted the fall.

D, N and R trains were operating with delays following the incident.

Additional reporting by Danielle Furfaro