A suicidal man jumped from a six-story Upper East Side building Tuesday — as dozens of witnesses on the ground below begged him, “Please don’t do it!”

The man plummeted six stories and landed broken and bleeding on the pavement, turning the shouts of compassion into screams of terror.

The man survived the fall, but was in grave condition at New York-Presbyterian Hospital.

“He just jumped,” said one witness. “It all went so fast. Oh, my gosh. We heard the splat. Thank God I never heard something like that in my life before.”

Before jumping at about 3:30 p.m., the unidentified man stood for about half an hour on the edge of the roof at 1491 Second Ave., near East 78th Street.

He yelled at a police officer: “Stay away from me! I don’t want to jump!” He appeared to be holding on to a wire. “At one point, he was threatening to cut the cable,” a witness said.

Finally, he turned, read something aloud from a piece of paper and leaped from the roof with a scream.