Qantas will reduce travelling time between Sydney and Johannesburg by more than two hours with the introduction of non-stop flights from January next year.

The Boeing 747-400 flights, operating five days a week, will take an average of about 14 hours 20 minutes for the 11,872 kilometre journey - one of the longest non-stop sectors on the Qantas network.

Deputy Chief Executive Officer, Geoff Dixon, said the service would be popular with First, Business and Economy Class passengers compared with the current journey of 16½ hours, four times a week via Perth.

Mr Dixon said the non-stop services were developed as part of a new codeshare agreement between Qantas and South African Airways.

"Under the agreement, South African Airways will place its code on the new Qantas flights between Sydney and Johannesburg and will discontinue operating between the two cities with its own aircraft.

"South African Airways will increase from four to five the number of return services it operates each week between Johannesburg and Perth. Qantas will codeshare on these services."

Mr Dixon said the codeshare agreement also included a number of domestic routes which would expand the network for Qantas in Africa and for SAA in Australia and New Zealand.

"Qantas will codeshare on SAA flights between Johannesburg and Cape Town, Durban, Harare and other destinations. SAA will codeshare on selected Qantas flights within Australia and between Sydney and Auckland, Christchurch and Wellington," he added.

The international sectors will be on sale from 1 November and the internal flights within Africa at a later date. The arrangements are subject to regulatory approval.