HILLSBORO, Ore. -- Hillsboro police officers said they cited 13 people who left their cars unattended with the keys in the ignition Tuesday morning.

Police said they patrolled downtown Hillsboro Tuesday between 5:30 and 6:30 a.m. after receiving numerous stolen vehicle complaints in the past week. Several of those complaints occurred in the early-morning hours when vehicles were left unattended with keys in the ignition, according to police.

Between 5:30 a.m. and 6:30 a.m. on Tuesday, officers said they found 34 vehicles left unattended with the engine running. Thirteen owners were beyond visual sight of their vehicles and were issued citations for leaving their car running, police said.

Officers said 21 other people received warnings.

Hillsboro has a city ordinance to prevent motor vehicles from being left running while unattended.