Two people were threatening each other with baseball bats near Fifth Street and Broadway, and when police responded they fled, Oakland police Officer J. Moore said.
The tube, which connects Oakland to Alameda, was closed as officers worked to apprehend the suspects. One was taken into custody at Seventh and Webster streets at 1 p.m., he said.
A short time later, police reopened the tunnel and were leaving the area, Moore said. He did not know whether the second suspect was also caught.
The Broadway exit from northbound Interstate Highway 880 was closed while police responded to the incident.
