Officers say they are now investigating two separate threatening calls.
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The venue was put on lockdown around 7:30 p.m., just as people were arriving to the show.
Entry and exit gates were shut down. Traffic in and out of the venue was stopped.
It caused a huge backup outside the area and on the foot bridge from BART as hundreds of concert-goers arrived.
Some told us it wasn't made clear to them what was going on. "Got here in line and right when we got to the front gate, they shut the gate on us and told us that there was a security situation they needed to handle before they would open it," recalled concert-goer Brett Strommen.
Investigators did not find any bombs during their sweep of the area.
The gates were reopened around 9 p.m. and the concert did finally go on after that.
Hans Zimmer has another show at the Oakland Arena on Wednesday.