STORY: Police and forensics personnel were seen cordoning off the scene of the crime on Wednesday night.
The next day, empty bullet casings were found on the ground outside the billiards hall.
The victims were reportedly all male, and nine of them were killed at the scene while one died of his wounds after being taken to hospital.
Guanajuato's governor Diego Sinhue Rodriguez said authorities were committed to finding those responsible for the attack and that justice would be served.
The federal security ministry said this week Guanajuato had seen the most murders this year among Mexican states, recording 2,115 victims between January and August.