The shoot-out is said to have begun when officers were carrying out investigations in the Mexican city of Saltillo.
Cops had stopped a vehicle for checks when the gangsters fired at them repeatedly, according to police reports.
As the situation escalated, a ‘Code Red’ was activated and back-up was scrambled to the scene, resulting in a 30 minute shoot-out.
It is believed that two cops also died during the confrontation.
Horrific photos from the aftermath show four bodies – three men and one woman – lying in a pool of blood which is splattered all over the walls.
Rifles can also be seen lying between the executed corpses.
Initial reports suggest the armed criminals belongs to the Noroeste Cartel, a local drug cartel.
Coahuila Governor Miguel Riquelme met members of the Security Secretary and the General Prosecution of the State in an urgent security meeting to talk about the incident.
A video taken from the scene shows cops taking position at a crossroads before dozens of gunshots can be heard.
The general prosecution released a statement saying the actions “were not an everyday occurrence” and that the police “will always act to maintain the integrity of citizens”.