MARYSVILLE, Ohio (AP) — Authorities are trying to find the source of carbon monoxide at an Ohio hotel that sent at least 11 people, more than half of them children, to a hospital.

Marysville Fire Chief Jay Riley told the Columbus Dispatch that everyone who was hospitalized had been in the pool area of the Hampton Inn. Authorities said a 911 call Saturday evening said a 2-year-old girl having fallen into the pool or was found unconscious there. More 911 calls soon followed about people unconscious or feeling such symptoms as dizziness and a burning in the throat, Marysville Police Chief Tony Brooks said.

Memorial Hospital spokesperson Melanie Ziegler said 11 people, five adults and six children, came to the hospital, seven brought by first responders and four coming in on their own.

She said two critical patients were stabilized and transferred to tertiary care facilities. Five others, listed as serious but stable, were also taken to other facilities. Four patients were treated and released. Brooks said two others were treated at the scene.

Officials said the building was evacuated, and Riley said any potential sources of carbon monoxide had been shut off. He said Sunday morning that he had no immediate update on the investigation.

A representative of the Hampton Inn Marysville said Sunday that officials were “fully cooperating with the local authorities as they investigate this incident.”

Marysville is about 30 miles (48 kilometers) northwest of Columbus.