Authorities say gunmen shot down a police helicopter in Apatzingán, Michoacán, killing the pilot and three officers.
Jalisco state prosecutor said Monday that local, state and federal authorities, including marines and soldiers, joined in the operation while investigators reviewed surveillance camera footage for clues.
Mexican criminal gangs used to avoid targeting the family members of their rivals. But in recent weeks, gunmen have mowed down fathers, mothers and children indiscriminately.
He said police and law enforcement are "what separates civilization from total chaos".
There are 21 people under arrest, according to the authorities.
The wounded were taken first to a local church and then to a hospital.
At least 11 poll-stations were assaulted.
José Mancha Alarcón, the state leader of the National Action Party said attackers burst into the home of the mayor of Acajete and set it on fire.
It started with Mexicans being publicly compared by presidential candidate Donald Trump to criminals and rapists. It escalated to ejections, to sucker punches, to pepper spray.
Waving U.S. and Mexican flags, more than 1,000 people turned out to protest Trump San Diego, a city which sits just 15 miles from the Mexican border city and where a third of residents are Latino.