After 20 people were killed in a slaughter during a cock fight, an American mother died and her teenage sister is in critical condition.

Melissa and her sister Arleth Silva, 16, were on vacation in Michoacan, Mexico, and were present at the event when gunfire erupted, according to family members who spoke to ABC7.

Melissa, a mother of four, was killed in the shooting, and Arleth was hit numerous times.

During the brutal massacre in the Las Tranjas district, seventeen men and three women were killed.

Arleth is currently in a Mexican hospital in critical condition. She was one of four people injured in the attack.

According to a GoFundMe page set up by a family member, she was shot once in the lungs and twice in the legs.

According to prosecutors, the gunmen organized the attack and arrived in the area in a stolen snack food company truck.

“The snack food company truck arrived, and several armed people in camouflage clothing got out,” a prosecutors’ statement said, according to the outlet.

“At the same moment, a bus that was outside the building was used as a blockade,” apparently to prevent victims from escaping or calling for help, it said.

A suspected gang of cartel men wearing military clothes broke into the busy event shortly after 10.30 p.m. on Sunday night.

Investigators discovered 15 vehicles that they believe belonged to the victims. One of them had stickers with a criminal gang’s logo on it.

Over 100 assault rifle bullet shells were also recovered sprawled across the ground by cops.

Drug cartels and other gangs had been battling in the neighborhood, according to prosecutors.

“There are indications that the attack involved a confrontation between criminal groups,” the federal Public Safety Department said in a statement.