Flight operations at San Diego International Airport were halted for nearly two hours Thursday morning after a security breach at Terminal 1 involving three passengers who left the terminal for a “smoke break,” a Harbor Police official said.

The passengers had already been screened and were waiting to board a flight to San Jose when they went out an exit to smoke cigarettes around 6:30 a.m. When they were done, they came back into the terminal through the same doorway, bypassing the security check. They then boarded their Southwest Airlines flight, said Harbor Police Sgt. Jose Torres.

The passengers’ reentry into the terminal triggered an alarm and prompted a “ground stop” at the airport, halting all operations while officials checked out the security breach.

Torres said all the passengers who had boarded the Southwest flight were taken off the plane and told to go through the security screening again. Officers also reviewed security footage of the smokers’ exiting and reentering the terminal.

The three smokers responsible for the security breach were issued misdemeanor citations and were not allowed to reboard their flight, he said.

Normal operations at the airport resumed at 8:17 a.m., Torres said. According to an airport spokesperson, a security hold on the Southwest flight was lifted at 8:30 a.m.