The robber entered the gambling hall of the Casino Monticello by a side door and shot a gun several times in the air, sparking panic among the customers.
The "clown" snatched almost 6 million pesos ($12,000) from one of the gamblers and left the building the way he came in at 5 a.m. Tuesday, according to a security camera.
Though the casino has not provided an official version of the incident, police detained one of the security guards, identified as Cristian Poblete, 26, who is suspected of being involved in the holdup.
Casino Monticello is located near the city of Rancagua and its largest shareholder is the France-based International Group of Gaming & Resorts.