ATLANTA (AP) — A concrete slab at a parking deck under construction in Atlanta collapsed Saturday — the second collapse at the site in as many days — sending a worker trying to shore up the structure plunging several stories below, authorities said.

The man suffered leg injuries after falling eight to 10 floors, Atlanta fire spokesman Sgt. Cortez Stafford said. The worker was taken to a hospital for treatment, and was alert and conscious, authorities said.

“He was on that concrete and rode it down as it collapsed,” Stafford said.

Authorities have stopped all work at the site and blocked off streets around it. The two collapses have compromised the structure and created a risk of additional falls, Stafford said.

The 3,000-space parking garage is being built at one of Emory University’s hospitals just north of downtown Atlanta. It was supposed to be completed next year.

On Friday, a section of concrete on the prefabricated parking deck partially collapsed, injuring six workers. A column on the 11th floor gave way, causing debris to fall onto the 10th floor in that initial collapse.

Stafford said Saturday that a construction problem, not a faulty design, was to blame for that first collapse.

Firefighters on Friday cut out one worker trapped under debris with saws and lowered him to the street, Atlanta Fire Rescue Deputy Chief Glen Riley said. The worker had leg injuries but never lost consciousness, Riley said. Other construction workers were injured but managed to walk away from the collapse, Riley told reporters at the scene. A firefighter also was taken to a hospital, with likely heat exhaustion, Riley said.

Firefighters raised concerns that more of the structure could yet collapse and fall onto Interstate 75/85, a busy freeway through the heart of the city. Parts of adjoining streets and a ramp to the freeway were closed as a precaution.

The garage is part of a major construction push at the hospital, including a new $470 million location for Emory’s Winship Cancer Institute, which is going up in a 17-story tower on a parcel separate from the parking garage.

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