PHILADELPHIA (Reuters) - Three workers were hospitalized in critical condition on Wednesday after a gas explosion in northeast Philadelphia that killed a colleague, a spokeswoman for Philadelphia Gas Works said.

The explosion Tuesday evening occurred in a high-pressure 12-inch gas main, said the spokeswoman for the city-owned utility.

The cause of the blast was unknown and under investigation, she said. The explosion occurred at about 8:30 p.m. in the Tacony section of northeast Philadelphia.

(Reporting by Jon Hurdle; Editing by Ellen Wulfhorst and Jerry Norton)