All passengers and crew escaped unhurt, they said.
The aircraft -- operated by the South African airline Comair -- was on a domestic flight carrying 94 passengers and six crew from the southern city of Port Elizabeth when the incident occurred around midday (1000 GMT).
"The aircraft was on the runway for a short period performing a standard landing when the crew noticed an unusual vibration which was followed shortly by the collapse of the left landing gear," said Comair CEO Erik Venter.
Flights at OR Tambo -- Africa's busiest airport -- were delayed by up to an hour due to the temporary closure of the runway following the incident, according to the Airports Company of South Africa (ACSA).
