Thick fog has disrupted about 25 flights at Melbourne Airport.
Domestic arrivals and departures have been affected.
Some international flights have been diverted.
Weather Bureau senior forecaster Dean Stewart says the fog is blanketing northern and eastern suburbs.
"It doesn't cover the whole of the Melbourne area, so some suburbs will start off sunny from sunrise this morning, and remain sunny," he said.
"The fog will start clearing, probably after about 8:00 or 8:30am (AEST)."
"In some areas it will take up until 10:00am before it's cleared completely," he said.
Mr Stewart also said there are reports that visibility is down to about 100 metres or so in some areas.
Qantas spokesman David Epstein says planes can now land.
"The weather's improving and we're expecting fine conditions for the rest of the day, so we've got to make up some ground," he said.
"There'll be a bit of a knock-on effect through the day, but we hope to recover that by the end of the morning."