The Bureau of Meteorology has issued a fog alert for road users across most parts of Melbourne with the thick blanket expected to cause some problems during the city's morning peak.
Duty meteorologist at the bureau James Taylor said northerly winds were not expected to clear the fog until 8 or 9am, with Melbourne's inner, northern, eastern and south-eastern suburbs the most affected.
Melbourne Airport had escaped the worst of the weather, but Essendon and Moorabbin airports were experiencing heavy fog patches this morning.
"Melbourne Airport has been quite lucky and has stayed fairly clear overnight," Mr Taylor said.
A spokeswoman for the airport said flight schedules had not been affected.
Mr Taylor warned drivers to reduce speed, keep headlights on and to keep a greater-than-usual distance between their vehicles and others on the roads.
The fog was widespread across Melbourne and the state, particularly in West Gippsland. Melbourne's eastern suburbs were experiencing the heaviest fog because the northerly breeze was lightest east of the city.
Mr Taylor said the fog was expected to clear between 8 and 9am, meaning peak-hour motorists should drive with caution.
Metro's website is reporting minor delays on the South Morang and Glen Waverley train lines.
Once the fog lifts, Melburnians could look forward to the warmest day since late May, said Mr Taylor, with clear skies, a light breeze and a top temperature of 18 degrees expected this afternoon.