Heavy fighting has started in northern Mexico between security forces and members of the powerful drug Sinaloa cartel after one of the group's leaders was discovered.
Ovidio Guzman Lopez was found during a routine patrol in Culiacan.
He is the son of drug lord Joaquin "El Chapo" Guzman, who has been sentenced to life in prison plus 30 years in the United States.
Guzman, 62, was found guilty in New York on 1
He escaped from a Mexican prison in a tunnel in 2015, but was later arrested. He was extradited to the United States in 2017.
Joaquin Guzman is a former leader of the Sinaloa cartel, which officials say is the largest drug supplier to the United States.
What happened in Culiacan?
The Government of the State alleges that Ovidio Guzman was found inside a house by a police patrol in a routine search.  It said that members of the cartel subsequently carried out the enormous attack in an attempt to take him away from the authorities.
It is believed that Ovidio Guzman, in his 20s, played a key role in the Sinaloa cartel after his father's arrest.
He was wanted in the United States on several drug charges, Mexican media report.
He was detained briefly before being released by police.
There were no official reports of deaths, but photos appeared apparently showing dead bodies on the city streets.
The Sinaloa State Government has stated that it is "working to restore peace and order in the high-impact incidents that have occurred in recent hours at various points around Culiacan," AFP reported.
"City under Siege" By 1965 1965 Mexico BBC correspondent Will Grant 19659004] Panic spread in the city as fighting continued between a number of machine guns – in pickups with machine guns mounted on them – and a large deployment of police and military.
In the midst of the chaos, a break in prison apparently happened, including a number of prisoners until the cartel tried to sow a larger one
What was El Chapo's role in the drug trade in Mexico?
El Chapo (or "Shorty") runs the Sinaloa Cartel in northern Mexico.
Over time, it has become one of the largest drug traffickers in the United States. In 2009, Guzman was listed on Forbes list of the richest men in the world at number 701, with an estimated value of $ 1 billion (775 million pounds).
He was accused of helping to export hundreds of tons of cocaine to the United States and conspiring to produce and distribute heroin, methamphetamine and marijuana.
He is also said to have used hitmakers to carry out hundreds of murders, assaults, abductions and torture of rivals.
Key contributors, including one former lieutenant, testify against Guzman.