SAN FRANCISCO (CBS) - The San Francisco Fire Department responded to a  manhole explosion in San Francisco's Financial District Saturday.  The blast was strong enough to shatter windows in nearby businesses.

It happened on Sansome Street between Clay and California.

PG&E trucks were on the scene.  One witness said he smelled smoke and saw flames.

According to PG&E it was an underground 'secondary failure'.  One firefighter CBS 5 spoke to said it was an electric vault that blew.

So far, there are no reports of any injuries.

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