The Australian Transport Safety Bureau (ATSB) says it is too early to say how close two Qantas planes came to mid-air disaster, in a near miss over South Australia yesterday.
A traffic control blunder resulted in one plane being given permission to fly towards the other, 20 kilometres west of Adelaide.
News Corporation is reporting that the Airbus A-330s came within about 200 metres of a collision.
But a bureau spokesman, Stephen Curry, says that has not been confirmed by the team investigating the incident.
"An investigation team is put together of suitably qualified and experienced people and they will be talking to the pilots involved, the air traffic crew, gaining recorded information from the aircraft," he said.
"It will be up to the ATSB commission to make that information available."
An air traffic controller has been stood down, which is standard procedure when an incident is under investigation.
Qantas confirmed two of its Airbus A330 aircraft were involved, but denied the incident was a near miss.
The airline says an onboard alert allowed the pilots to overcome a "loss of separation" between the aircraft.
Passenger Gary Martin said he say another plane below his own when they were travelling over South Australia.
However, he says he did not think anything was amiss.
"I saw a plane going underneath us to the left, somewhere in South Australia I'd suggest," he said.
"I don't think anybody knew, I saw it and didn't care. They know what they're doing."
Janet McLean was on the plane that arrived in Sydney and says she did not think there was a major issue during the flight.
"There was a sensation of certainly dropping down, like one drop and then another drop and then we must have just levelled back out," she said.
"I sort of thought, I presumed, an air pocket - but it really wasn't bumpy like an air pocket, it was a smoother sort of drop.
"Apart from that, no, we had a beautiful landing."