SYDNEY, Aug. 14 (Xinhua) -- The head of Australia's transport safety investigator said on Friday that the agency is trying to understand why a safety incident involving two planes at Sydney Airport on Sunday was reported late.

An Air New Zealand flight arrives at Sydney Airport in Sydney, Australia, on Feb. 21, 2022. (Photo: Xinhua)

The Australian Transport Safety Bureau (ATSB) said on Thursday night that it has commenced an investigation into a runway incursion incident on Aug. 9 involving Qantas flight QF728 to Ayers Rock Airport in central Australia and Virgin Australia flight VA555 to Perth.

A statement from the ATSB said that air traffic control cleared the Virgin Australia flight for a full-length runway take-off from Sydney around 10 a.m. local time on Sunday. As the crew applied thrust, they observed the Qantas flight begin crossing the runway ahead of them.

The Virgin Australia flight subsequently came to a stop before being re-cleared to commence take-off.

ATSB Chief Commissioner Angus Mitchell told Australian Broadcasting Corporation radio on Friday that he was not notified about the incident until Thursday.

"The two aircraft didn't come within really probably around a thousand meters of each other. But, notwithstanding that, it shouldn't have occurred," he said.

"We're still trying to understand exactly what the delay in the reporting to us was."

The ATSB said on Thursday that the Qantas crew involved in the incident on Sunday reported having received clearance to cross the runway.

It said that investigators would interview involved parties and review data.

The incident was the third runway incident at Sydney Airport in two weeks.

Earlier on Sunday, a Jetstar Australia flight was forced to brake suddenly to avoid colliding with a Qatar Airways jet that was being towed, while on July 27, a QantasLink flight and a Qantas plane were involved in a near-collision.