Perth has shivered through its coldest September in more than 20 years while overnight temperatures dropped to a 72-year record-breaking low.

And it looks like spring will continue to stay in hiding with the forecast for October expected to also be below average.

Bureau of Meteorologist spokesman Neil Bennett said only four days in September reached above 20 degrees – equalling an unenviable record set in 2009.

"We've had the coldest September since records started at the Mt Lawley (Perth metropolitan) station in 1994," he said.