Captain Julia Claassen said that a group of armed suspects entered the casino just after midnight on Monday and headed straight to the vault.
Claasen could not confirm the number of people in the gang but some told Talk Radio 702 on Monday morning there could have been about 20 people.
The men ordered the casino's 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 the gang assaulted six patrons in the meantime.
"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," said Claasen.
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. – Sapa