San Francisco Public Utilities Commission crews are trying to determine what caused a water main break near Balboa Park in the city’s Mission Terrace neighborhood this afternoon.

A 12-inch water main ruptured shortly after noon near the intersection of Ocean and San Jose avenues, SFPUC spokesman Tyrone Jue said.

Crews were able to shut down the main within 40 minutes of the break, Jue said.

The incident has caused the closure of westbound Ocean Avenue while crews determine what caused the break. The eastbound lanes of the street are still open, as is the entrance to northbound Interstate Highway 280, Jue said.

Sonic equipment is being used by the crews to determine the source of the leak, he said.

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