There has been heavy fighting in northern Mexico between the security forces and members of the powerful Sinaloa drug cartel after one of the group's leaders was discovered.
Ovidio Guzmán López was found during a routine patrol in Culiacán.
He is the son of drug lord Joaquin "El Chapo" Guzmán, who was sentenced to life in prison plus 30 years in the US, BBC reported.
Guzmán, 62, had been found guilty in New York of 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.
Joaquin 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?
The state government say Ovidio Guzmán was found in a house by a police patrol on a routine search.
It says cartel members subsequently launched the huge attack in an attempt to wrestle him back from the authorities.
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.
He was briefly detained before being released by the police.
There have been no official reports of fatalities, but pictures have emerged apparently showing dead bodies on the streets of the city.
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".
What was El Chapo's role in Mexico's drug trade?
"El Chapo" (or "Shorty") ran the Sinaloa cartel across northern Mexico.
Over time, it became one of the biggest traffickers of drugs to the US. In 2009, Guzmán entered Forbes' list of the world's richest men at number 701, with an estimated worth of $1bn (£775m).
He was accused of having helped export hundreds of tonnes of cocaine into the US and of conspiring to manufacture and distribute heroin, methamphetamine and marijuana.
He was also said to have used hitmen to carry out "hundreds" of murders, assaults, kidnappings and acts of torture on rivals.
Key associates, including one former lieutenant, testified against Guzmán.
BDST: 1103 HRS, OCT 18, 2019