Gun owners who carry their arms in public must also carry the relevant firearm licence and their identity document, Gauteng police warned on Tuesday.

"These documents are very important as they may at any moment be confronted by law enforcement officers during police operations," Superintendent Eugene Opperman said.

"... they then need to immediately produce it. The licence they carry must be for the specific firearm they have in their possession. The identity document is needed to prove a person's identity as the licence alone cannot perform that function."

In routine stop and searches carried out around the province over the past 24 hours, 13 people were arrested and eight illegal firearms were recovered, Opperman said on Tuesday morning.

"One such incident on Monday involved the arrest of four suspects after information was received that the men were planning to commit an armed house robbery in Alberton," Opperman said.

"The vehicle used by the suspects was stopped on the Old Vereeniging road in Alrode South. On searching the vehicle police found a stolen revolver in the car. All four men were arrested."

In an unrelated incident, Springs police investigating an alleged kidnapping case went to an address in 3rd street.

On searching the premises they found an illegal firearm hidden between the mattress and base of a bed.

One person was arrested, said Opperman.