The Midtown high-rise fire that killed an elderly couple was sparked by the wife’s lit cigarette, police sources told the Post.

The fatal Saturday morning blaze that killed 85-year-old Mary Merow and her husband, John Merow, 89, started when Mary allegedly fell asleep on the couch with a lit cigarette in her hand, police sources said.

The fire started around 5:20 a.m. in their ninth-floor apartment of the tony River House on East 52nd Street.

Mary suffered severe burns and could not be saved, authorities said. Meanwhile, John was rushed to NewYork-Presbyterian/Weill Cornell Medical Center, where he was pronounced dead.

Three firefighters, including two with serious but non-life-threatening injuries, were taken to NYU Langone Medical Center, an FDNY spokesman said.

The FDNY has not yet said whether there were working smoke detectors inside the apartment.