Carbon monoxide leak reported at Pennsylvania day care, 28 hospitalized: Fire officials

Twenty-eight people were taken to hospitals with minor to moderate injuries following a carbon monoxide leak at a Pennsylvania day care Tuesday morning, fire officials said.

The Happy Smiles Learning Center in Allentown had 27 children and eight staff members inside at the time, according to Allentown Deputy Fire Chief Christian Williams.

The day care has been evacuated, officials said.

Crews from UGI Utilities responded and shut off the gas line from outside the building as a precaution, UGI Utilities spokesman Joe Swope said.

Williams said a cause has not yet been determined. According to Swope, UGI believes the leak was caused by a faulty heating unit and a blocked ventilation system.

ABC News' Alex Faul and Victoria Arancio contributed to this report.