An unscheduled power outage forced airlines to check customers in manually at OR Tambo Airport which led to a slight delay in check-ins, the Airports Company South Africa said on Wednesday.

Acsa spokesperson Solomon Makgale said the power outage during the afternoon and into early evening was not connected with "load shedding".

Generators immediately "kicked in" and all critical areas of the airport, including runway lighting, were functioning normally, Makgale said.

The outage lasted about two and a half hours and led to minimal inconvenience, he said.

Acsa was investigating the cause of the power outage alongside municipal councillors.

All queues and delays had been resolved by 7.30pm on Wednesday, he said.

Sapa