Two school children were among the 18 killed when two buses collided on the R61 between Cradock and Graaf-Reinet in the Eastern Cape on Saturday, Arrive Alive said.

"The death toll has increased to 18. Earlier we reported that 16 people had died but two others have died in hospital," spokesman Tshepo Machaea.

Fourteen people were seriously injured in the crash. They have all been transported to hospitals in the area.

One of the buses was carrying schoolchildren to an event in Graaf-Reinet when it collided with a bus carrying passengers from Cape Town to Mthatha.

It remains unclear whether the accident was a head-on collision or a side-swipe. Transport department spokesman Ncebo Kumbaca said the deputy minister Sindisiwe Chikunga and Eastern Cape transport MEC Thandiswa Marawu were expected to visit the injured soon.

The Democratic Alliance says it is shocked by the accident.

DA MP Donald Smiles, in a statement, extended his condolences to the families of those killed.

"Our hearts and prayers are with them," he said.