It happened around 8:25 a.m. on Ewing Street between Terhune and Cuyler roads.
Investigators say a milling machine hit the gas line, sparking a fire.
PSE&G was called out to depressurize the line. There was also a diesel fuel leak, prompting a hazardous materials response.
Several residents of Ewing Street were evacuated until the situation was brought under control.
Firefighters hosed the machinery down with foam, but the fire continued to burn for several hours, until it was finally extinguished before 6:00 p.m..
There was no word of any injuries.
