A heatwave scorching its way across much of Australia this weekend could have Sydney's summer temperature records poised to topple.

After a relatively mild start to the week, parts of the city's west will swelter through 40-degree-plus temperatures on Friday, Saturday, Sunday and into Monday.

Hot and dry conditions are forecast across New South Wales on Friday, with severe fire danger forecast for the greater Hunter, greater Sydney, central ranges, northern slopes and north western regions.

As the weather heats up, residents near fire-prone areas across NSW should prepare a bushfire plan, NSW Rural Fire Service spokesman Greg Allan said.