Clean-up operations for a major water main break in Southwest Center City were disrupted this morning when a gas line broke, apparently under the weight of collapsing asphalt.

Firefighters hooked hoses up to hydrants in the area around South 21st and Bainbridge Streets as PGW crews worked to close the gas main.

The major water main break near 21st and Bainbridge Streets on Sunday night forced the evacuation of several blocks of residents - some by boat - and left a cleanup job that could continue for days, city officials said.

This morning, the intersection was "gone," turned into a "rather large sinkhole," city water department spokesman John DiGiulio said.

About 7:30 a.m., the gas leak in the sinkhole forced water department crews to suspend work while the Fire Department took over, DiGiulio said.

After about three hours, the gas leak was fixed, but then electricity became a concern. Underground wires would need rerouting from the sinkhole so water department crews could continue work, said PECO spokesman Ben Armstrong.

In addition, six homes had their electrical service cut off for safety reasons, such as wet or damaged wiring.

The first sign of water trouble came around 8 p.m. when neighbors began reporting seeing steam coming up through manholes - followed by gushing water.

Soon the streets were flooding. In some places, the water was knee-deep or higher with a south-flowing current

Homeowners scrambled to seal basement windows with plastic. Firefighters used boats to rescue some stranded neighbors.

Water service to homes in a wider swath of South Philadelphia was affected. Some Center City residents reported also losing water.

More than three dozen people were evacuated, and at least seven were taken to the E.M. Stanton School at 17th and Christian Streets, according to Dave Schrader, chief spokesman for the American Red Cross' regional office.

By 1:30 a.m., crews completed the painstaking process of completely shutting off the 48-inch transmission main along 21st Street, DiGiulio said. It feeds water into smaller mains throughout South Philadelphia.

By then, waters that had risen as high as three feet in streets around 21st and Bainbridge were down to a few inches at most.

Water service was soon restored and residents began returning to homes, as claims adjusters went door to door overnight, cataloging the damage.

Area residents with continuing water problems, and those with damaged homes not yet seen by the claims adjusters, should contact the water department at 215-685-6300, DiGiulio said.

As for why the massive transmission main broke, DiGiulio said, "We believe it's likely almost a 100 years old if not more."

Neighbors reported that there had been construction in the area around 21st and Bainbridge.

More investigation is needed to make a final determination. "It's not our typical break season," DiGiulio said.

Schrader urged residents to throw out any food that had been soaked by flooding.