A second case of avian flu has been confirmed at a farm in Standerton, the Department of Agriculture, Forestry and Fisheries said on Monday.

"The virus is the same strain as the initial case reported, but the two farms are not directly linked, meaning this is a separate introduction," said department spokesperson Bomikazi Molapo.

The farm had been placed under quarantine and over 25 000 infected birds would be culled.

Eggs were not allowed to move off the farm.

The initial case saw highly pathogenic avian influenza (HPAI) H5N8 confirmed in a broiler breeder site in Mpumalanga on Thursday, June 22.

Molapo said the ban of live hens (including roosters) was still in place to allow the department to assess the extent of the outbreak.The ban would be observed for 14 days. The situation would then be reassessed.

"It takes approximately four days for the infected bird to show clinical signs of the disease. We have put this measure in place to prevent further unintended spread of the influenza."

HPAI is a rapidly spreading viral disease that can infect many types of birds and is highly contagious.

It exists naturally in many birds and can be transmitted by coming into contact with infected animals or through ingestion of infected food or water, the department explained.

Commercial and backyard farmers were urged to report large numbers of birds dying to the nearest state vet.

This would allow the department to send veterinary officials for a follow-up investigation and to collect samples.