ALLENTOWN, LEHIGH COUNTY (WBRE/WYOU) — More than two-dozen children were rushed to a local hospital after a carbon monoxide leak at an Allentown daycare center.

Fire officials were called to Happy Smiles Learning Center around 7:30 a.m. Tuesday morning for a child who was unconscious.

Firefighters say their equipment detected high carbon monoxide levels inside the building.

Authorities say about 25 children and eight staff members were taken to the hospital to be checked out.

Capt. John Christopher of the Allentown Fire Department told WFMZ that every ambulance in the city had responded to the daycare center Tuesday morning. The outlet added that officials were calling the incident a “level 1 mass casualty” incident, meaning hospitals in the area should prepare to be overwhelmed.

All impacted are in stable condition.

UGI crews are trying to find the source of the leak and what caused it. Officials say there is no carbon monoxide detector in the building.

Legislation passed last month requires all childcare centers in Pennsylvania to have CO detectors but it is not in effect yet.

The director of happy smiles said there were already plans to install a detector.