Gunmen killed eight people and injured five others in the city of Guamuchil, 1,130 km northwest of Mexico city, authorities said on Sunday.
A group of attackers traveling in three vehicles shot passengers in four cars stopped by a red light on a busy street in Guamuchil of the state of Sinaloa in the early hours of Sunday.
The victims included two 17-year-old boys and a 12-year-old girl, authorities said.
The incident was allegedly related to the ongoing wave of drug-related violence in the state.
In an earlier attack on Saturday, six other gunmen shot dead a police officer and took dozens of hostages in a shopping mall in the city of Mazatlan in Sinaloa state, prosecutors of the state said.
Sinaloa is one of the Mexican states plagued by drug trafficking and drug-related gun killing.
On July 10, a group of armed men killed 16 people including police officers in Culiacan, capital of Sinaloa.
The Mexican government declared the war against drug trafficking in the country. President Felipe Calderon has sent some 36,000 federal troops to main areas controlled by drug gangs, especially Sinaloa.
Violence related to drug trafficking has claimed 2,000 lives in Mexico so far this year.