Gunmen opened fire on four cars on a busy street in the city of Guamuchil, killing eight people, according to local news media.
The government news agency Notimex reported that Sinaloa state officials said three teenagers were among those killed in the early morning attack. The local newspaper El Debate said police found about 300 shells at the scene.
On Saturday, assailants killed a state police officer in the port city of Mazatlan and hid in a shopping mall.
The group seized hostages but freed them in a deal to escape.