State Fire and Rescue Service spokeswoman Viktorija Gribuste told Latvian Radio's evening news show the leak was reported at around 5pm Monday evening in the Jaunmarupe suburb of the capital.
Despite arriving on the scene quickly, two men were found to have been overcome by fumes and could not be revived despite the best efforts of rescuers.
"When firefighters arrived at the scene, one employee had already been brought outside the premises with no signs of life, and while searching the premises, rescuers found another person. They were transferred to the care of medical professionals but unfortunately they could not be saved... rescuers are continuing to search the site," Gribuste said.
Police are investigating the cause of the fatal gas leak.