At least one woman hurt in San Francisco explosion

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SAN FRANCISCO (Reuters) - An explosion in San Francisco's central financial district on Friday injured at least one woman, and police closed several city blocks while they searched cause of the blast. A police spokesman said it may have been an underground explosion. An electrical transformer could have been the cause of the explosion, one official said.

Witnesses reported a large bang shortly before 10 a.m. near Post and Kearny streets in front of a Ralph Lauren store in the central business district.

The blast caused lights in office buildings in the area to flicker. One woman was sent to the hospital with injuries, police officer Jason Hui said.

Officials evacuated buildings in a one block perimeter of the blast and roped off streets leading into the area. Several hundred workers milled around.

Dozens of firefighters and a number of fire trucks rushed the area, as did local utility workers.

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Explosion In PG&E Vault Rocks Downtown SF - CBS

The source of the explosion is not known at this time, but PG&E spokesman Paul Moreno confirmed that the location of the incident was in an electrical underground vault that houses transformers and other equipment.

"Exactly what caused the explosion, we don't know yet," Moreno said.

But San Francisco Fire Chief Joanne Hayes-White emphasized there is no cause for alarm.