The building is located at Howard and Beale Streets.
Video in the media player above is from a previous update
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It's one of 71 buildings previously identified by city inspectors in need of additional window inspections.
Police closed nearby streets out of fear glass could fall to the sidewalk.
San Francisco police say the closure began around 9:30 a.m.
Inspectors later determined the crack was on the inside of the window.
And it appears the crack is not weather related.
There is no report of glass falling from the building.
Officials say this is the latest window in an office building to crack.
The situation is reminiscent of windows blown out during the Bay Area storms earlier this year.
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San Francisco is requiring inspections and in some cases extra glazing in 71 skyscrapers after glass fell from high-rises during an intense storm in March.
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