A stranger repeatedly punched a 64-year-old man — breaking his nose and fracturing his face — in an unprovoked attack inside a Brooklyn train station over the weekend, cops said.

The victim was on a Manhattan-bound R train at the Prospect Avenue station just after 1 p.m. Sunday when the assailant approached and began pummeling him, police said.

The suspect bolted from the train at Prospect Avenue.

The victim, who suffered a broken nose, facial fractures and bruises, and scraped knees, was taken to Brooklyn Methodist Hospital for treatment.

The suspect, shown in surveillance footage released late Monday, is still on the loose, cops said.