Crews were running a check on the 16-inch PVC pipeline below Balboa Avenue in the Tecolote Canyon area by charging it with water when it failed about noon, city spokeswoman Monica Munoz.
The personnel were able to quickly halt the overflow, which caused no structural flooding.
One of two eastbound lanes in the area was expected to remain off-limits to through traffic between Clairemont Drive and Mount Culebra Avenue into the evening hours to allow for excavation and repairs, Munoz said. Motorists were advised to avoid the area if possible.
The cause of the mishap, which occurred during a pipeline-replacement project, was not immediately clear.