Repair crews have isolated the flow of a water main break that caused a major outage in some Philadelphia neighborhoods, leaving residents in Chestnut Hill, Mount Airy, Roxborough, and West Oak Lane without water.

A 30-inch transmission water main broke around 5 a.m. Monday near the intersection of Cherokee Street and Hartwell Lane, causing the widespread outage, said Brian Rademaekers, spokesperson for the department. Any water main over 16 inches is considered a transmission main, which carries large amounts of water to other mains. That caused such a large area to be impacted by the outage, he said.

Late Monday morning, repair crews had stemmed the flow of water, and pressure would be returning to residents’ homes gradually, he said. It was unclear how many residents had been affected by the outage.

Many residents complained on social media of having no water and reaching a dead end on the phone when calling to report the service disruption. As crews worked to isolate the break, Rademaekers said updates would be posted on the department’s Twitter, @PhillyH2O.

“At this point it’s just a matter of time,” he said. “There’s not much customers can do except wait.”