A man was stabbed during a fight with an apparent stranger inside a downtown Brooklyn train station early this week, cops said.

The victim, a man in his 20s, was knifed in the right arm during the clash on the southbound No. 4 train platform at Borough Hall around 1:20 a.m. Sunday, police said. 

The assailant, who also appears to be in his 20s and isn’t believed to have known his victim previously, ran out of the station after the bloodshed, cops said.

The victim was taken to NYU Langone Hospital – Brooklyn, where he was listed in stable condition. 

It’s not known what sparked the fight that led to the stabbing.

In a separate attack on the rails earlier this month, a 31-year-old woman was beaten on board a northbound A train at the 88th Street station in Ozone Park, police said Thursday morning.

The victim was riding the train around 3 p.m. April 10 when she noticed a group of young teens smoking in one of the cars, and moved to a different one, cops said. 

Two members of the group — a boy and girl — followed her into that car and started arguing with her, police said. 

The exchange of words turned violent when the duo punched and kicked her multiple times on the train before the fight spilled onto the platform, authorities said. 

A good Samaritan intervened and pushed the suspects off the victim, cops said. 

The victim got back on the subway, while the assailants stayed on the platform and boarded the next northbound A train, police said. 

The victim suffered pain and swelling to her body. 

Police were still looking to track down the attackers Thursday.