Also injured were another utility employee and a firefighter, officials said. The cause of the explosion, which destroyed nearby buildings and torched cars, is under investigation.
Jim Campoli, 61, told The Philadelphia Inquirer that he was at home, listening to the radio, when a police officer banged on his door and told him to evacuate. He said he and several people were standing on the corner watching utility and fire crews working when the fireball burst into the sky.
The force of the explosion knocked down a man standing with Campoli, he said.
"Oh, man! It just blew up the whole street," Campoli said. The Southeastern Pennsylvania chapter of the American Red Cross opened a comfort center to help residents of the 15 to 20 dwellings affected by the blast. The Red Cross helped about 75 people who visited the center during the evening. All were allowed back home by early Wednesday or found a place to stay, the Red Cross said.
The newspaper said those evacuated included about 24 people from a senior care home.
Jim Smith, a supervisor in the Philadelphia Fire Department's communications center, said a company was dispatched after the center received a report of an odor of gas in the neighborhood.
He said the leak turned out to be "fairly serious" and an additional crew was sent to investigate. He said that's when the blast occurred from some unknown ignition source.
The utility is providing counseling services to employees.