A stranger slashed a 66-year-old man in the face in an unprovoked attack on a Midtown train early Thursday, cops said. 

The victim was riding a southbound No. 6 train pulling into the 33rd Street station around 3:20 a.m. when another man, believed to be in his 40s, stood up and appeared to be stretching, authorities said. 

As the suspect stretched, he slashed the innocent straphanger on the left side of his face without saying a word, cops said. 

The attacker then got off the train, police said. 

The victim got off at the next stop and was taken to Bellevue Hospital with non-life-threatening injuries. 

Police were still looking for the assailant, who they said had a dark complexion and was wearing dark clothes, hours later.