Mexican security forces have arrested one of the sons of notorious drug kingpin Joaquín "El Chapo" Guzmán, local officials say.
They say this happened in the western city of Culiacán, the stronghold of the powerful Sinaloa drug cartel.
The capture of Ovidio Guzmán López triggered heavy gun battles between suspected cartel members and the security forces across the city.
In July, Guzmán was sentenced to life in prison plus 30 years in the US.
Guzmán, 62, had been found guilty by a court in New York on 10 charges, including drug trafficking and money laundering.
He escaped a Mexican jail through a tunnel in 2015, but was later arrested. He was extradited to the United States in 2017.
Guzmán is a former head of the Sinaloa cartel, which officials say was the biggest supplier of drugs to the US.
What happened in Culiacán?
Ovidio Guzmán, said to be in his 20s, is believed to have played a key role in the Sinaloa cartel, following the arrest of his father.
He is wanted in the US on several drug-related charges, Mexican media report.
News of his arrest on Thursday led to heavy shooting across the city, which is the capital of Sinaloa state.
The Sinaloa 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 Culiacán", AFP news agency reports.
Mexican President Andrés Manuel López Obrador said he would make a statement later on Thursday.
What was El Chapo's role in Mexico's drug trade?
"El Chapo" (or "Shorty") ran the Sinaloa cartel across northern Mexico.