Nineteen people were killed in Mexico's northern state of Sinaloa late on Friday in a run of related shootouts between police and gunmen, Reuters reported.
Armed men in pickup trucks approached police on a major highway near the city of Mazatlan and began firing at them, according to press releases from the state police and state attorney general's office.
Aided by federal forces, the police fought off the attackers and pursued them to the nearby town of La Amapa, where the gunfight resumed.
Seventeen people were killed in the shootouts with police, and another two were killed nearby in what appear to be earlier, related shootings, the attorney general's office said.
Five police suffered gunshots and are in stable condition, with two of those officers suffering head wounds, according to state police. Sinaloa is a major battleground in Mexico's drug war.
Found at the scene were 16 semiautomatic rifles, seven handguns and a shotgun, the attorney general's office said.
The state is home to the Sinaloa cartel, whose most well known boss, Joaquin "El Chapo" Guzman, was extradited to the United States in January to face trial.
Police killed 17 people for every officer lost in gunbattles in 2014, according to a study by Mexico's National Autonomous University, a number experts say is consistent with excessive use of force.
In 2015, Mexican police executed nearly two dozen suspected gang members after ambushing them at a ranch near the small town of Tanhuato in the violent western state of Michoacan, one of the worst abuses by security forces in a decade of grisly drug violence.
Some 30,000 people have disappeared in Mexico since drug violence increased sharply around 2007. Since former president Felipe Calderon sent the army out to battle drug gangs at the end of 2006 more than 150,000 have been killed.