SAN JOSE -- A bomb threat Thursday against the Santa Clara County Superior Court system spurred the morning-long evacuation of three downtown court buildings and a precautionary bomb sweep of all 11 county courthouses, producing a brief scare but no explosives, authorities said.

No injuries were reported in the episode, which began about 9:40 a.m. when a court administration building at Market and West Saint James streets received a phone call with someone saying "there's a bomb in the building," Santa Clara County Sheriff's Sgt. Kurtis Stenderup said.

Court spokesman Joseph Macaluso said the threat did not name a specific court building. But because the threat was received at the complex on West Saint James, the two "Community Towers" were evacuated, as well as the Park Center Plaza courthouse on Park Avenue. Local streets were also shut down.

The rest of the county's 11 courthouses, spanning Palo Alto to Morgan Hill, were swept for potential explosives as a matter of protocol, Macaluso said.

The sweep quickly cleared all of the locations of any dangerous devices except for Park Center Plaza, where family law court is housed. Around 12:30 p.m., the court announced that a suspicious package was found and summoned the sheriff's bomb squad to investigate.

About half an hour later, the court said that the package was deemed not to be dangerous. Around the same time, all of the standing evacuations and surrounding road closures were rescinded.

Normal operations resumed at all of the locations except for the Park Center Plaza site, where the afternoon calendar for Thursday was canceled.

The source of the threat remains under investigation by the Sheriff's Office, which provides security for the county courts.

Contact Robert Salonga at 408-920-5002. Follow him at Twitter.com/robertsalonga.