Aliens or balloons in New York sky?

All those theories about yesterday's mystery UFO sightings over Manhattan are about to go pop.

A Westchester elementary school believes the puzzling orbs floating over Chelsea were likely a bundle of balloons that escaped from an engagement party they held for a teacher.

"UFO? They're crazy those are our balloons!" said Angela Freeman, head of the Milestone School in Mount Vernon. "To me it was the most automatic thing. But it's all over YouTube."

A parent was bringing about 40 iridescent pearl balloons to the school for language arts teacher Andrea Craparo when the wind spent a bunch away around 1 pm.

"They looked big and they were all together, so it looked like one UFO," said fourth-grader Nia Foster aged nine.

Awestruck gawkers began calling officials from the New York Police Department (NYPD).

An hour later,u00a0 the Federal Aviation Administration (FAA) started an inquiry about the mysterious flying objects appeared over Manhattan.

Meteorologists with the National Weather Service said the wind was blowing south at the time which would make the engagement balloon theory possible.

Police have said they believe the puzzling objects were likely balloons.

The sky was very clear at the time, making high-flying objects extremely visible from the ground.

Also, helium-filled balloons tend to change shape at high altitudes as the gas expands making them look abnormal from below, experts say.

However, author Stanley Fulham, a retired officer had another theory. He recently published a book predicting the world's major cities would be visited by UFOs on October 13.

He was unavailable for comment.