Australia's transport safety regulator said on Friday it had launched an investigation into a fourth incident involving air traffic control at Sydney Airport in less than a month after two planes were directed towards the same intersection on the ground.

Two Qantas aircraft were cleared to use the same taxiway and only stopped after crew observed the planes approaching – the fourth similar issue since July 28.

Investigators are examining an incident on Tuesday where two Qantas flights were given clearance to take clashing routes.