Air tests at a New Hampshire school where more than 20 people showed symptoms of carbon monoxide poisoning have turned up no elevated levels of the gas.

Derry Fire Chief George Klauber says firefighters responded to St. Thomas Aquinas School at 10:50 a.m. Wednesday along with 10 ambulances.

He says carbon monoxide meters found no elevated levels by Wednesday afternoon. He says another source of the illnesses has not been determined.

Three hospitals were alerted. Parkland Medical Center spokeswoman Pat Collopy says she doesn't know of anyone in critical condition.

About 220 students in preschool through eighth grade were taken to a nearby church.