About three tons of mandrax were seized on Sunday, Captain Mack Mngomezulu said.
The drugs were discovered after a fire broke out on a plot in Crystal Park.
When the fire department arrived at the house the gate was locked and firefighters had to force it open.
"Four people were seen running away from the premises after the gate was opened," Mngomezulu said.
Firefighters put out the fire and found a lab which was used to manufacture drugs.
"We suspect that an explosion was the cause of the fire. In the garage there was a mixing machine, chemicals, and substances to make drugs," he said.
Mandrax was left to dry out on the tennis court on the premises.
A case of manufacturing drugs was being investigated by police.
No arrests had been made.