AUBURN — A man working on a heating and cooling unit on the roof of the Auburn Mall fell through a skylight at about 1:30 p.m. Wednesday, dropping to the cement floor at center court.

George Beam, 43, of Biddeford sustained “serious” injuries to his head in the roughly 20-foot drop, authorities said.

The outside contractor from Atlantic Comfort Systems had been on the mall roof to work on the building’s heating and cooling system when he apparently mistook a Plexiglas bubble skylight for a snowdrift, fire Chief Frank Roma said. Beam was taken to Central Maine Medical Center in Lewiston.

Beam was listed in critical condition Thursday morning.

According to an eyewitness, Alyssa Black, she heard a loud “thud” and then “saw a gentleman fall from the roof onto the cement floor.”

Black works at nearby Kay Jewelers, and said she ran to the store to call 911 while others gathered around the man to try to help. Black said he fell on his face and stomach, and people hesitated to touch him and cause further harm. Someone checked to see if he was breathing, and Black estimated emergency workers arrived within three to five minutes.

“People were pretty shocked,” Black said. “There’s a couple of older folks who sit by (the former Asian Gourmet) and have lunch, and all of a sudden this gentleman falls through the roof.” She said it was clear he fell from the roof because snow came down with him as he fell.

Bits of the skylight also came down as he fell, and scattered on the mall floor.

“It was very traumatizing to see,” Black said. “I really hope that poor gentleman and his family — I hope he’s OK.”

Rescue workers took the man to Central Maine Medical Center about 10 minutes after the initial call, according to mall employees and witnesses. Black said the man was unconscious right after the fall but that he tried to fight the EMTs as they were working to load him on a stretcher.

Another eyewitness, Kristi Anderson of Lewiston, was at the mall shopping with her children, ages 8 and 11. They were walking out of Bath & Body Works and “at first thought it was tile that was falling, but then we saw that there was a man lying face-first on the floor.”

She said people immediately jumped up to help, others called 911, and she tried to shield her children from the sight.

“It took a while for him to move,” she said, as a crowd of people gathered around him.

“The EMTs and Auburn Police Department were awesome at how quick they got there and how they handled the situation,” Anderson said. “They were amazing.”

Ben Patten of Winthrop said he heard a “bang” as he was strolling nearby waiting to meet his mother for dinner.

By the time he looked at where the sound came from, he could see chunks of snow falling through the dark, square hole in the ceiling. A man dressed in brown work clothes and a hat was lying on the floor.

He was slipping in and out of consciousness, Patten said. He struggled with EMS workers.

“He wanted to get up,” Patten said.

The cause of the accident was under investigation. The Occupational Safety and Health Administration was called.

Calls placed to Mark Tuller, CEO and president of the Biddeford-based Atlantic Comfort Systems, were not returned.

Roma said the accident is a good reminder to be cautious while working on a roof.

“The lesson in this for all of us now, with the amount of snow that we’ve had this winter, is that the roofs can be very treacherous for slipping or in the case of even private homes that have skylights, not knowing that something is there and accidentally taking the wrong step,” he said.