Mexican security forces on Thursday arrested one son of jailed drug kingpin Joaquin "El Chapo" Guzman in an operation that triggered intense fighting.
Heavy gunfire rocked Culiacan, a city of 750,000 people, in sustained clashes that left blazing vehicles strewn across the street and sent terrified residents running for cover.
Security Minister Alfonso Durazo confirmed the arrest of a man identifying himself as Ovidio Guzman, one of the sons who assumed partial control of the notorious cartel run by their father until he was extradited to the United States in 2017.
Images carried on Mexican television showed army and police personnel under assault by men armed with heavy weapons.
President Andres Manuel Lopez Obrador said his security cabinet was holding a meeting and would soon give further details on the situation. Sources in the Sinaloa state government speaking on condition of anonymity said police officers had been wounded.
They also said an unknown number of inmates had escaped from the Aguaruto prison in Culiacan amid the chaos.
The state government said it was "working to restore calm and order in the face of the high-impact incidents that have occurred in recent hours in various points around Culiacan." It called on residents to "remain calm, stay off the streets and be very attentive to official advisories on the evolving situation."