San Antonio police are investigating reports of a suspect seen fleeing from the alley, Police Chief William McManus said.
McManus said police got a call late Saturday night about shots fired. Officers canvassed the area, and found holes on the building and multiple shell casings.
No one was injured, but police officers inside heard gunshots strike the building, he said.
Authorities have a description of a suspect seen running from the alley, and are working to get more details.
Police vehicles have cordoned off the area as the investigation continues.
The shots come as police departments nationwide remain on edge following Thursday night's killing of five officers
in Dallas by a gunman.
Authorities named Army veteran Micah Johnson, 25, as the lone gunman in the Dallas attack. He ambushed the officers during a march protesting the fatal police shootings of two African-American men the same week in Minnesota and Louisiana.
Officials said Johnson expressed anger over the shootings by police, and said he wanted to "kill white people, especially white officers."
Police on alert
Since the shooting in Dallas on Thursday,
police agencies nationwide have added security measures.
Major cities including Chicago, New York, Philadelphia, Cincinnati and Las Vegas, ordered its officers to pair up with partners to increase visibility.
New York's mayor, Bill De Blasio, placed all foot patrol officers in pairs and said two officers will be posted outside all police stations.
For its part, Dallas police tightened security throughout the city because of an anonymous threat, spokeswoman Monica Cordova said Saturday without elaborating.
Hours before the San Antonio incident, Dallas police officers searched the parking garage of their headquarters Saturday afternoon after a report of a suspicious person.
The search yielded no suspects or strange items, Dallas police said.
Dallas police killed Johnson early Friday, and are trying to determine whether he acted alone in the police ambush.
While authorities have said they believe he was the sole gunman, what's unclear is whether he conspired with others or how long he had planned an attack.