January was Australia's hottest month in more than 100 years of records, with the mean temperature across the country for the month exceeding 30 degrees for the first time.

Bureau of Meteorology senior climatologist Dr Andrew Watkins said it had been extraordinarily hot right around Australia.

"The exceptional story here is temperatures," he said.

"One of the key records that we've seen has been the hottest overnight temperature on record - the hottest minimum temperature on record - 36.6 degrees was the lowest it got to [one night] in Borrona Downs in north-west NSW."