The city of Culiacan in northern Mexico, known for drug gang activity, witnessed an outbreak of violence overnight, gunshots were heard and streets were blocked, Sinaloa state authorities said Thursday.

As a result, local authorities ordered the suspension of activities and public transportation, Reuters reported.

Roads were reportedly blocked by burning vehicles. Mexican security forces arrested the son of imprisoned criminal Joaquín “El Chapo” Guzmán, but then released him to avoid threats of violence from his supporters.

The mayor of Culiacán urged residents to stay indoors.

Mexican President Andrés Manuel López Obrador said that a federal police operation was underway in the state.