An 80-year-old woman jumped to her death from an Upper East Side apartment building Saturday — and was decapitated when her body hit the side of the building on the way down, witnesses and officers said.

The unidentified woman jumped from the 28th floor of the Tony Park Regis Apartments around 3:30 p.m., police said.

Witnesses said her body became entangled in something on the side of the tower, which had numerous balconies, and was decapitated.

“I just stopped when she was laying there, she had no head,” a resident of the building told the Post on Saturday.

“The head and arm were cleanly severed on the other side, they ended up on the terrace.”

The NYPD did not immediately release the identity of the victim or a possible motive for suicide.

Her clothes were stuck to a fence at the base of the building, which was bent by the impact, witnesses said.

“Everyone started running towards the body, but she was gone,” said a 23-year-old who witnessed the immediate aftermath of the fatal incident.

“Her body ended up there, but her head and leg hit the fence there. You can see it’s bent, there were clothes and blood stuck in it.”

The elderly woman was the second jumper to plunge to her death on Saturday.

Police said a 52-year-old man jumped from a 17th-floor balcony of his 22-story building in Chelsea around 5 a.m., apparently killing himself.

The unidentified man was pronounced dead at the scene and police have not released the identity of the victim.

A distressed woman, believed to be the woman, was seen sobbing and visibly shaken outside 315 West 25 St. after the fatal incident.

If you are struggling with thoughts of suicide or experiencing a mental health crisis and live in New York City, you can call 1-888-NYC-WELL for free and confidential crisis counseling. If you live outside the five boroughs, you can call the 24/7 National Suicide Prevention hotline at 1-800-273-8255 or visit SuicidePreventionLifeline.org.