The construction worker fell at a site on West 17th Street, officials said. View Full Caption DNAinfo/Trevor Kapp

UNION SQUARE — A construction worker was critically injured Wednesday morning when he fell four stories and was impaled on steel bars at a site near Union Square, witnesses said.

The man, whose name and age were not immediately released, was on a ladder installing some drywall for the ceiling of 34 W. 17th St., near Sixth Avenue, about 8:25 a.m., when he tumbled down an elevator shaft into the basement, FDNY and Department of Buildings officials said.

He landed on three pieces of rebar that pierced his stomach, thigh and groin, witnesses said.

"He wasn't even touching the floor. The rebar was holding him a foot off the ground," said James Apolito, 31, an elevator technician at the site.

"He was conscious. He was moaning. It was shocking. It was bad," Apolito said.

He also had a large bump on his head the size of a softball, the elevator technician said.

"I kept trying to tell him not to move. We were getting materials to support him," he added.

Crews were able to free him, but he still had a piece of steel in him when they wheeled him to the ambulance, a witness said.

"He was on a stretcher and had a piece of rebar in his stomach. It was sticking out eight to 10 inches," said Chuck Hayes, 68.

"Paramedics took him out and put a mask over his face. I couldn't tell if he was conscious."

The man, who coworkers said is in his 40s, was initially listed in critical condition, the FDNY said. He was treated at Bellevue Hospital where he was upgraded to stable condition, officials said.

"He's a nice guy, quiet guy," Apolito said.

"I hope he survives."

The building, which was previously used for manufacturing, was bought for $20 million by developers Atkins & Breskin who are making it into apartments, according to a 2015 Real Deal report.

Buildings officials said the permits were in order for the site, but they'd still be shutting it down for investigation.

Police were also investigating the site, officials said.

The contractor at the site, New Empire Builder Corp., did not immediately return requests for comment.