"Our mission in Islamabad in Pakistan, which is also accredited in Afghanistan, has informed us that eight South Africans were among the dead in the explosion which occurred in Kabul early this morning," foreign affairs spokesperson Nelson Kgwete told AFP.
"They worked for a private aviation company," he added.
The group were all believed to be men, Kgwete said.
"Our mission in Islamabad is working on the identity of the men and contacting their next of kin."
Tuesday's attack by a woman suicide bomber was the deadliest single attack claimed to avenge a US film that has sparked a week of bloody protests across the Muslim world.
More than 30 people have now been killed in the violent backlash over a YouTube trailer for the film Innocence of Muslims.