The thick fog that covered Sydney for the second consecutive day on Wednesday has started to lift up, but air carriers continued to advise travelers of potential flight delays in the coming hours.

A Qantas spokesperson told ABC Radio that Wednesday's scheduled flights could be delayed by as much as four hours, even more. Some flights were likewise expected to be diverted to Brisbane and Melbourne.

"Please check your flight status," a Qantas tweet read.

Web sites of Virgin Australia and Qantas likewise advise that several flights from Melbourne, Canberra and Brisbane have been cancelled or delayed by more than 45 minutes.

At least 13 international flights failed to land in Sydney airport on Wednesday morning. The first plane that was able to touch down hit ground at 6:49 a.m. Seven other overseas flights landed only by 8 a.m.

Ben McBurney, meteorologist from Weatherzone, said light winds and cooler night-time temperatures combined with high moisture levels resulted to the white fog over Sydney.

Ferry services, which were initially cancelled at 5.30 a.m., have resumed at 9 a.m. However, a spokeswoman for Transport Management Centre warned delays would still occur within the day.

Weather experts said the fog could return on Thursday and Friday mornings.

Ferry and airline passengers were advised to contact their respective carriers since each are affected differently by the mayhem.