New York — A young woman who lost an arm and a leg after being struck by a downtown train in Harlem was subway surfing when she fell under the train’s wheels, NYPD sources said Thursday.

The unidentified victim, who is between 17 and 20 years old, was spotted by witnesses trying to scramble to the top of an express No. 3 train at the 135th St. subway station at about 6:10 p.m. Wednesday when she fell on the track bed, police said.

The train rolled over part of her body, severing her arm and leg, police said.

EMS rushed the woman to Harlem Hospital, where she remained in critical condition. Cops were trying to identify her Thursday.

Last month, a 13-year-old girl was killed and a 12-year-old girl critically hurt when they fell while subway surfing together in Queens, police said.

Following the Oct. 27 tragedy, New York City Transit President Demetrius Crichlow implored parents and children to take the consequences of subway surfing seriously.

“This is no game,” Crichlow said. “There’s no reset at the end. There’s no restart when a person falls. I remember playing Nintendo. At the end of the game you just restart it. That doesn’t happen. This is a life or death matter. There is no do-over.”

A few days after the fatal hit, Mayor Adams implored residents to call 911 if they see anyone subway surfing. The NYPD also announced they will be flying drones over elevated train lines to spot people attempting to subway surf.

Six people have died from subway surfing and 181 arrests have been made as of Oct. 27, police said.