A UPS employee opened fire at a San Francisco package delivery facility today, injuring four and prompting a massive police response in a neighborhood near downtown, officials said.

UPS spokesman Steve Gaut said that an employee fired inside the facility before the drivers were sent out to do their normal daily deliveries.

Gaut said four people were injured and that he believed the shooter 'turned the gun on himself'.

Gaut did not have immediate information about anyone's condition. Nor did Brent Andrew, spokesman for Zuckerberg San Francisco General Hospital, which had received the victims.

He did not know exactly how many people. Auto shop owner Robert Kim said he heard about five to eight rapid gunshots.

The next thing he knew, he said, 'a mob of UPS drivers' was running down the street screaming 'shooter, shooter'.

Police confirmed the shooting at the facility in the Potrero Hill neighborhood, about two-and-half miles from downtown San Francisco but didn't release further information.

UPS employees were later led out in a line by officers next to a highway.

They walked away calmly with emergency vehicles nearby and gathered nearby outside a restaurant.

The shooting led to a massive police response and a shelter-in-place warning for the surrounding area. Police advised people to avoid the area. -- Agencies