Toxic fumes have killed at least 10 people who were trying to clean a sewage pump station in a town in central Mexico.

Atotonilco de Tula town president Julio Cesar Angeles says eight people were pulled from the station dead. Two others died at a hospital in Pachuca. One person is still missing.

The group of community volunteers entered the station early Saturday.

Survivor Rafael Ramirez said Sunday that the fumes were stronger than normal, but he and his companions didn't think they were deadly.

After about 15 minutes, men began to pass out. Ramirez says he tried to help them but had to get out before he lost consciousness too.

Officials are trying to determine why the group was cleaning the pump station.