San Francisco Mayor Ed Lee immediately took to Twitter, decrying the shooting as a "senseless act of violence."
"We are always saddened by the loss of life to gun violence," Lee tweeted. "Any shooting is one shooting too many."
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SAN FRANCISCO, CA - JUNE 14: A San Francisco police officer stands guard at the scene of a shooting at a UPS facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employess at a UPS facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
Eric Risberg/AP
UPS employees hold their hands in the air as police storm the roof of the UPS warehouse in the Portero Hill neighborhood of San Francisco. San Francisco police confirmed a shooting took place at the sprawling facility. (June 14, 2017)
Kevin Wood via Twitter
From an apartment across the street, a neighbor captured a photo of UPS employees gathered on the roof of their workplace after an armed employee opened fire in the building, fatally shooting 3 coworkers before turning the gun on himself. (June 14, 2017)
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Police gather outside a UPS facility in San Francisco after a gunman opens fire. (June 14, 2017)
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A host of UPS employees are moved from a company facility in San Francisco after a shooting breaks out. (June 14, 2017)
Stephen Lam/Reuters
People hold their hands above their heads as they evacuate after a fatal shooting at a United Parcel Service (UPS) facility in San Francisco, California. (June 14, 2017)
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UPS employees are moved from a company facility in San Francisco after a shooting breaks out. (June 14, 2017)
Cass SeaBass/ treesdancealone via Instagram
UPS employees evacuate from a facility in San Francisco after a gunman opens fire. (June 14, 2017)
Eric Risberg/AP
UPS workers gather outside after a reported shooting at a UPS warehouse and customer service center in San Francisco on Wednesday, June 14, 2017. San Francisco police confirmed a shooting at the facility in the Potrero Hill neighborhood but didn't immediately release information on injuries or the shooter.
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UPS employees are moved away from a company facility in San Francisco after a gunman opens fire. (June 14, 2017)
Police gather outside a UPS facility in San Francisco after a gunman opens fire. (June 14, 2017)
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UPS employees are moved from a company facility in San Francisco after a shooter opens fire. (June 14, 2017)
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Police post up outside a UPS facility in San Francisco after a gunman opens fire. (June 14, 2017)
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Police walk around a UPS facility in San Francisco after a gunman opens fire . (June 14, 2017)
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Police walk around a UPS facility in San Francisco after a gunman opens fire . (June 14, 2017)
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Police walk around a UPS facility in San Francisco after a gunman opens fire . (June 14, 2017)
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Police walk around a UPS facility in San Francisco after a gunman opens fire . (June 14, 2017)
Scott Budman/NBC Bay Area
Police cars park outside San Francisco General Hospital and Trauma Center after a shooting at a UPS facility. (June 14, 2017)
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A press conference was held near the UPS facility in San Francisco. (June 14, 2017)
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SAN FRANCISCO, CA - JUNE 14: San Francisco firefighters work a triage area at the scene of a shooting at a company facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employees at the facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JUNE 14: A San Francisco police officer stands guard at the scene of a shooting at a UPS facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employess at a UPS facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JUNE 14: UPS workers are escorted by San Francisco police at the scene of a shooting at a UPS facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employess at a UPS facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JUNE 14: UPS workers are escorted by San Francisco police at the scene of a shooting at a UPS facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employess at a UPS facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JUNE 14: A San Francisco police officer looks into a garage at the scene of a shooting at a company facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employees at the facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JUNE 14: UPS workers are escorted by San Francisco police at the scene of a shooting at a UPS facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employess at a UPS facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
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SAN FRANCISCO, CA - JUNE 14: A San Francisco sheriff deputy stands guard at the scene of a shooting at a UPS facility on June 14, 2017 in San Francisco, California. A gunman opened fire on employess at a UPS facility, killing at least 2 and injuring several others. (Photo by Justin Sullivan/Getty Images)
Scott Wiener, representing San Francisco on the California State Senate, shared his thoughts and prayers with the victims and their families.
"Praying for the shooting victims at the UPS facility in San Francisco," he tweeted. "Way too many shootings in this country. It's depressing."
Toney Chaplin, the assistant police chief for San Francisco Police Department, said the deadly shooting at a UPS facility “is a tragedy that has touched many lives today.”
California Senator Kamala Harris echoed her colleagues' heartache and called for an end to gun violence.
"The news of a senseless act of gun violance at the San Francisco UPS facility is heartbreaking," she tweeted. "Please keep the community in your prayers."
Jane Kim, a member of the San Francisco Board of Supervisors, also offered a similar sentiment by writing #gunviolencemustend in her post-shooting tweet.
Stay tuned for more details regarding this developing story.
