The concrete ceiling of a posh Park Avenue co-op collapsed on Saturday morning, sending out a whoosh of dirt and debris, but only minor injuries.

The dust-up at 1065 Park Avenue near East 87th Street happened in the midst of a three-year, $2 million renovation of the 30-story building’s lobby and outdoor plaza.

Workers last week installed a concrete board and stucco drop ceiling.

“The concrete board was evidently too heavy,” said Malcolm Karlin, a resident who sits on the board.

“Evidently something went wrong. It just couldn’t hold. It all came down around 9:30.”

Two construction workers were hurt, but not seriously, officials said.

“Some people on the third floor heard it, a little rumble,” Karlin added. “Look, were lucky. It’s Saturday morning. Half the people in the building are gone for the summer. We’re lucky.”

After the collapse, well-heeled residents rolled up their sleeves to clear a path through the debris.

Several stood on sidewalk surveying the damage: bales of insulation, cracked Jerusalem stone and a tangle of exposed electrical wiring.

The building was once home to TV personality Regis Philbin and actress Polly Bergin.