Sydney residents are about to shiver through the coldest period of the year with minimum temperatures set to plummet to single digits for the next four days.

It will be a chilly start to Friday with a minimum of 9 degrees on the coast, 6 degrees in Penrith and 4 degrees in Campbelltown, according to the Bureau of Meteorology.

The weekend will be even colder with a minimum of 7 degrees in Sydney on Saturday and Sunday.

Penrith residents can expect a cold start to the day on Saturday with a minimum of 4 degrees, before dropping to 3 degrees on Sunday.