One police officer has died and another has undergone surgery after they were shot in an incident in San Diego.
San Diego Police Department said the shooting occurred late last night, but provided no further details.
There was no immediate word on what sparked the violence in the south-east of the Californian city.
Police have been searching the area for suspects and urged residents to stay indoors.
Police Chief Shelley Zimmerman said the injured officer was expected to survive after coming out of surgery.
Video footage from the scene shows officers out in force with numerous squad cars with emergency lights flashing lining a street, officers on foot, and a helicopter buzzing overhead.
The police department said in a tweet that one suspect is in custody and other possible suspects are being sought.
The shooting comes as police across the US remain on high alert following the killing of officers in Dallas and Baton Rouge, Louisiana, earlier this month.