Twelve people were killed in a shooting at a bar in central Mexico on Saturday, local authorities said, with growing cartel violence making the region one of the country's most dangerous.

Industrial Guanajuato state has become the site of a raging dispute between two rival groups -- the Santa Rosa de Lima and Jalisco New Generation cartels -- known for carrying out drug trafficking and fuel theft, as well as other crimes.

Police believe Saturday's attack took place when an armed group entered the bar in the city of Irapuato at around 8 pm (0100 GMT) and opened fire on customers and staff.

At least six men and six women were killed, and three others were injured, the municipal government said in a statement, without specifying the identity of the attackers or their motives.

The body of one victim was found outside next to a motorcycle, while the rest of those killed were discovered inside the bar, police said.

The assailants are being hunted by state police, the army, the prosecutor's office and the National Guard, the municipal government said.

The attack is Guanajuato's second mass shooting in less than a month.

In September, armed attackers killed 10 people in a pool hall in the state's Tarimoro municipality.

And earlier this month organized crime groups massacred 20 people, including the mayor, at the town hall in San Miguel Totolapan, in the nearby state of Guerrero.

Authorities say there have been 2,115 homicides in the region between January and August.

Mexico has recorded more than 340,000 murders, most of them attributed to criminal organizations, since the launching of a controversial military anti-drug offensive in December 2006.