The intersection of 17th and Vermont streets in San Francisco is shown in a Street View image from Google Maps.
San Francisco police are responding to a shooting near the Bayshore Freeway, the department said in a tweet. "We've accepted some and we're expecting more". Sources tell ABC7 News at least three people were shot at the facility and multiple victims have been transported to the hospital.
Another man in a UPS uniform also said the gunman was a UPS employee. Officers with drawn rifles stood in the street. San Francisco police are advising residents in the area to shelter in place.
Witnesses say they heard several shots and saw people running out the UPS building.
Police had an unidentified person in custody following an apparent workplace shooting at a UPS facility in the city's Potrero Hill neighborhood.