A father watched helplessly as his 20-year-old son plunged out of their Harlem apartment window Saturday, police sources said.

The victim, identified as Jonathan Walton, jumped at around 2:10 p.m. from the sixth-floor window of the building, cops said. His dad frantically dialed 911 for help, but it was too late.

Walton was rushed to Harlem Hospital, where he was pronounced dead a short time later, authorities said.