By Steve Beck, Mark Abrams

PHILADELPHIA (CBS) – Firefighters have cleared an elementary school in Northeast Philadelphia after a noxious odor was detected inside the school early Thursday morning. As a precaution, students were evacuated and taken to a nearby school.

The incident happened at the James J. Sullivan Elementary School in the 5300 block of Ditman Street in the city’s Frankford section.

According to school officials, the building was evacuated after the detection of an unknown and noxious odor.

As a precaution, approximately 600 students were evacuated and taken to the Warren G. Harding Middle School on Wakeling Street. Students were later sent home for the day.

Nobody was sickened by the odor because students and staff were not allowed into the structure after a school employee discovered the problem before classes began.

Members of the fire department’s hazardous materials team wearing protective suits went into the school and took air samples. But they detected no harmful substance and they were unable to find the source.

The incident remains under investigation.