Mexico mass shooting: 12 killed, over 20 injured as gunmen open fire at religious celebration (WATCH)

Gunmen killed 11 people and injured at least 20 in an attack during a religious festival in a central Mexican city plagued by gang-related violence, authorities said Wednesday.

Bloodstains were seen on the ground and bullet holes in the walls following the shooting Tuesday night in Irapuato in Guanajuato state during celebrations marking the Nativity of John the Baptist.

"It was chaos. People put the wounded into their cars and rushed to hospital to try to save them," a witness told AFP, asking not to be named due to safety concerns.

A 17-year-old was among those killed, along with eight adult men and two women, the Guanajuato state prosecutor's office said, vowing that the crime would not go unpunished.

Security forces were searching for the perpetrators of the "cowardly act," while officials were providing psychological support to those affected, the Irapuato municipal government said in a statement.

President Claudia Sheinbaum condemned the shooting as "deplorable," adding that authorities had launched an investigation.

Speaking at her daily news conference, Sheinbaum described the incident as a "confrontation" without giving details about the circumstances or the victims.

Mexico mass shooting: Horror caught on camera

A video shared online shows the moment when gunfire erupted as people were dancing and socializing, causing panic.

Guanajuato state Governor Libia Dennise condemned the bloodshed and expressed "solidarity and condolences" to the victims and their families.

Guanajuato is a thriving industrial hub and home to several popular tourist destinations, but it is also Mexico's deadliest state due to gang turf wars, according to official homicide statistics.

Criminal violence, most of it linked to drug trafficking, has claimed around 480,000 lives in Mexico since 2006 and left more than 120,000 people missing.

Much of the violence in Guanajuato is linked to conflict between the Santa Rosa de Lima gang and the Jalisco New Generation cartel, one of the most powerful in the Latin American nation.

Guanajuato recorded more than 3,000 murders last year, the most of any Mexican state, according to official figures.