At least 20 people were killed when gunmen attacked a local bar in Monterrey in Mexico, authorities said.

The attackers, who came in two pick-up trucks and one car, stormed into the bar "El Sabino Gordo" and opened fire on the patrons, they said.

"Up to now, we have found 17 bodies inside the bar and three more outside," an official from the prosecutor's office told AFP on condition of anonymity.

The assailants numbered at least 15, according to one local resident. They also strafed a hot dog stand with three people standing in front of it.

The bar is located on Villagran Street, in the center of a busy nightlife district.

Monterrey has been the site of a bloody confrontation among leading Mexican drug cartels feuding over lucrative narcotics supply routes leading to the United States.

Earlier Friday, 11 bodies with gunshot wounds were found in Chalco, a suburb of the Mexican capital, police said.

Mexico has been convulsed by a massive crime wave, with some 37,000 people killed in battles among rival drug cartels and between traffickers and security forces since 2006, when the government launched a military crackdown.

The National Commission for Human Rights (CNDH) said in a report on Wednesday that it had documented some 523 human rights violations since 2005, including murders, attacks, kidnappings and arbitrary arrests.