More than two dozen people were rushed to hospitals in eastern Pennsylvania on Tuesday following an apparent carbon monoxide leak at a day care center, officials said.
Allentown firefighters were originally called to the Happy Smiles Learning Center, a little more than 50 miles north of central Philadelphia, after getting a report about an unconscious child, said Capt. John Christopher, a department spokesperson.
When firefighters arrived, their monitors for carbon monoxide in the atmosphere immediately went off, Christopher told reporters at the scene.
That prompted them to evacuate 25 children and eight staffers as paramedics declared the scene to be a mass casualty incident, according to the spokesperson.
They took 27 patients to four hospitals, he said.
A “vast majority” of the hospitalized were children of “pre-K to elementary school-age,” Christopher later told NBC News. All of those hospitalized were stable and none of them were listed in serious condition, he said.
There were no carbon monoxide monitors in the building, officials said.
UGI Corp., the region's natural gas supplier, said it traced the leak to "a malfunctioning heating unit and blocked venting system," according to a company spokesperson.
"Gas was turned off to the facility until repairs can be made," according to the company. "UGI ensured there was no gas leak in the vicinity."