Police responded to a report at about 8 a.m. that a passerby saw a duffel bag leaning up against a bench near the intersection of Market and Battery streets, police spokesman Officer Albie Esparza said.
While investigating the bag, officers shut down Market Street to vehicles and pedestrians between Davis and Sansome streets, and Battery Street between Mission and Pine streets, Esparza said.
Several officers and bomb squad officials then examined the bag. They ran it through an X-ray machine before deciding there were no suspicious devices inside and cut it open.
"We basically found clothing," Esparza said. He said the owner of the bag has not been located, and police may keep the bag or destroy it.
Police reopened the streets at about 11:30 a.m., Esparza said.
No one was injured during the incident, and the bag has not been connected to recent reports of suspicious devices in the U.S., Esparza said.
"There's nothing to indicate that this was related to any other incident," he said. "The reason we responded like this is that public safety is our number one priority."