A police reservist and two security guards were shot and critically wounded in an armed robbery at Carnival City on the East Rand early on Monday morning, police said.
Captain Julia Claassen said that a group of armed suspects entered the casino just after midnight and headed straight to the vault.
Claasen could not confirm the number of people in the gang, although eNCA reported that the gang was made up of about 25 people.
The men ordered the casino patrons to lay on the floor and then used a hammer and a grinder to open the vault.
The gang removed an undisclosed amount of money.
A shift manager alerted police, but in the meantime the gang assaulted six patrons.
"When they tried to flee, a shootout ensued between the suspects and police, in which two security guards and one reserve officer, from Brakpan police station, were shot."
The three wounded men were admitted to hospital in a critical condition.
Claasen said police were searching for the suspects, but no arrests had been made by 7.30am.