A security alert delayed domestic aircraft flights out of Cape Town International Airport on Sunday morning, the Airports Company South Africa (Acsa) said.

Acsa would not specify the nature of the alert - whether it was terror related - or how it was brought to the attention of the authorities.

All passengers had to be "re-screened" and the departure area thoroughly "swept", Acsa spokesperson Deidre Hendricks said in a statement.

She refused to answer telephonic questions about the alert and in response to written questions, added only that hand luggage was still being allowed on board.

Hendricks would not elaborate on what was sought in the sweep, how it was conducted or whether anything was found.

"As far as the alert is concerned, it is standard security procedure to follow particular processes, which in this instance involved re-screening," was all she would say. She declined to reveal whether the area was evacuated.

Hendricks said domestic departures were delayed by an hour-and-a-quarter. It was not known how many flights were involved.

Processing of passengers resumed later, she said.

As an added security measure, Acsa was carrying out "thorough searches" at boarding gates prior to boarding.

This was "an additional process" to the screening point "for added security". - Sapa