FREMONT, Ohio (AP) — A concrete roof partially collapsed Wednesday at a sauerkraut factory in northern Ohio, killing one worker and injuring three, authorities said.

The roof collapsed as workers for B&W Welding were replacing support columns inside the small building at the Fremont Co., Police Chief Tim Wiersma said. Crews were still trying to remove the body of the man who died, 35-year-old Nate Kern.

A second rescue team was called in Wednesday night to relieve the first team. Workers set up lights so they could see in order to knock down a wall to get to a room connected to the area that held Kern’s body, Wiersma said.

Todd Michael, 44, was trapped in the debris with his legs pinned for about four hours before he was rescued. Wiersma said he didn’t know the extent of Michael’s injuries but that it appears he will survive.

While he was trapped, Michael told rescuers how to move the concrete and deal with the rubble, Wiersma said.

‘‘He was trying to save himself,’’ he said.

Michael was taken by helicopter to the University of Toledo Medical Center, where officials would not release his condition, citing patient confidentiality.

A third B&W worker was taken to St. Vincent Medical Center, where he was listed in fair condition Wednesday night. One Fremont Co. worker who was struck in the head was taken to a hospital for treatment and released, authorities said.

The cause of the collapse remained under investigation. A woman at B&W said the owner was not available to comment.

No one else was in the factory at the time of the collapse, which was in a roughly 50-by-100-foot, two-room building, Wiersma said.

Rescuers used a crane to lift up the collapsed roof.

One firefighter was treated for heat exhaustion amid temperatures that climbed into the mid-90s.

The Fremont Co. is about 40 miles southeast of Toledo in an industrial area with several buildings. It began in 1905 as a sauerkraut manufacturer and later expanded to make tomato-based products, including ketchup. It also sells and distributes a line of barbecue sauce, according to the company’s website.