An off-duty police officer was punched in the head as he rode a Queens subway in an unprovoked attack Wednesday night, cops and law enforcement sources said.

The 31-year-old was riding a southbound F train when the suspect assaulted him near the Union Turnpike-Kew Gardens subway station, police said.

The suspect punched the off-duty NYPD officer multiple times in the head, cops and sources said.

The suspect, who appeared to be in his 30s, has not been arrested, police said.

There is no indication the suspect knew the victim was a police officer, according to sources.

The off-duty officer refused medical attention at the scene. The investigation is ongoing, cops said.