Sydney and large regions of eastern Australia posted their hottest July on record and there's little sign the long-running above-average temperatures are about to recede.

The Harbour City posted average daytime temperatures of 19.9 degrees last month, according to Weatherzone.

Sydney has never had a July as warm during the daytime as the month just ended. Credit:John Veage

That was 3.5 degrees above the typical conditions for July, eclipsing the previous record high of 19.5 degrees set in 2013, according to Bureau of Meteorology data. Many sites, such as Penrith, Camden and Bankstown, also posted records.

Nationally, it was the second warmest July on record for maximums, trailing only 2017.