Gunmen killed 17 people and injured 18 in a pre-dawn attack Sunday on an outdoor party near the northern Mexico town of Torreon, officials said.
The gunmen arrived in cars and without saying a word began to open fire, police said. Most of the victims were aged between 20 and 30.
Officials feared the death toll could rise because some of the injured were in critical condition.
Police found more than 120 cartridges at the scene, which was on the outskirts of the city in Coahuila state, bordering Texas.
Officials were not immediately able to give a motive for the attack, which they said appeared drug-related.
The region around Torreon is a transit point along smuggling routes to the United States.
Thousands of people have been killed in drug-related violence across Mexico over the past four years.