Drivers were being urged to take it easy on the roads as a heavy fog covered Sydney on Monday morning.

Ten domestic flights were cancelled and one international flight was diverted as Sydney residents woke up to a thick blanket of fog, reducing visibility to 50 metres in some parts of the greater metropolitan area.

The worst affected area was the south-west, where visibility was down to 50 metres at Camden.

Visibility dropped to 100 metres in Campbelltown in the south-west and Richmond in the north-west. 

The CBD and Sydney Airport were not affected as badly, with visibility down to 200 metres.

Weatherzone meteorologist Graeme Brittain​ warned drivers to take extra care on the roads.

"Those on the roads should be careful due to the low visibility," he said. "Drive slowly and keep the lights on."

The fog is expected to lift later this morning as the temperature rises.

Sydney residents can expect a mostly sunny day on Monday with a top temperature of 20 degrees.

The sunshine won't last, with more rain forecast for the rest of the week, according to the Bureau of Meteorology.

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