The Bureau of Meteorology predicts extreme heatwave conditions for much of the state, with the temperature set to top 40 degrees across the west and in coastal areas.

NSW Rural Fire Service Deputy Commissioner Peter McKechnie has urged people to have a fire plan ready and prepare their properties.

"This is the first time since the devastating season last year we've seen widespread elevated fire danger," he said on Friday.

"Know what to do if a fire threatens you, know where you'll go."

The southwest will experience the worst of the fire conditions on Saturday, before the scorching weather moves through Sydney, the Hunter Region and north coast on Sunday.

Mr McKechnie said grassland areas west of the Blue Mountain ranges were of particular concern, as were the windy conditions.

"These are dangerous conditions, fires will start easily and they'll spread very quickly," he said.

Last summer's bushfires destroyed 2476 homes, claimed 26 lives and burned 5.5 million hectares of land.

Sydney is forecast to hit 39C on Sunday, while some records are expected to be broken in western NSW.

A cooler gusty change is tipped to cross the state on Sunday and into Monday, but temperatures are expected to rise again on Tuesday.

The cool front is likely to pick up dust which could reach Canberra, the BOM says.

NSW Health wants people to take extra precautions before the heatwave and check on vulnerable friends and family, particularly the elderly, to make sure they're coping.

"Our bodies are not acclimatised to the heat just yet as we enter summer. The heat we'll see over the weekend will affect everyone," NSW Health's Dr Adi Vyas said.

He said people keeping cool in public areas like shopping centres and libraries would have to maintain social distancing.

"This is a COVID pandemic year, so there's a few things we might have to do differently," Dr Vyas said.

Australian Associated Press