At least six police officers in Philadelphia were wounded in a shooting in the Nicetown-Tioga neighborhood, authorities told the local CBS affiliate.
Another officer was wounded in a car crash while traveling to the scene.
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The officers were taken to Temple University Hospital and other medical facilities to being treated for non-life-threatening wounds.
"Police were first called to the scene for narcotics activity," said police Capt. Sekou Kinebrew.
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Blocks were cordoned off. Police said one suspect was in custody and a second was barricaded with a weapon and apparently still in a position to fire at officers.
One report on Twitter said officers were trying to communicate with the shooter, "imploring him to surrender and avoid further injuries."
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There were no other details available on the person in custody.
"There is a large police presence and citizens are advised to avoid the area. Several blocks around the scene have been cordoned off. Most of North Philadelphia is in gridlock due to the police presence," the CBS affiliate said.
The NBC station in the city reported the first call for help for officers asked for "everything you got. SWAT, long gun."
The firefight, involving hundreds of shots, erupted when a warrant was being served on one site in the neighborhood.
The nearby Health Sciences Center Campus at Temple was locked down for a time.
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Traffic was in gridlock because of streets being shut down.