The arena construction site in downtown Allentown was evacuated Friday morning due to a natural gas odor, officials said.

Officials were notified of the odor shortly after 9 a.m., said Capt. John Christopher, Allentown Fire Dept.

The source of the odor remains under investigation, according to Christopher.

A 69 News crew on the scene said workers were allowed back into the building at just after 9:30 a.m.

Becky Eshbach, a spokeswoman for Reading-based UGI, told 69 News that the utility's personnel were called to the scene, but the issue appeared to be in a fuel line, not UGI equipment.