Last month, near-surface land and sea temperatures were 0.45 degrees higher than the 1981-2010 average, eclipsing the previous biggest anomaly for August of 0.33 degrees set last year.

The record warmth, if confirmed by other agencies such as NASA, would make August the sixth month so far in 2015 that has set a new heat record.

The massive El Nino weather event that continues to build in the Pacific is helping to drive temperatures higher against a background warming caused by climate change, climatologists say.

This year's El Nino is already the strongest event since the biggest on record - which sent worldwide temperatures spiking in 1997-98 - and is expected to continue to intensify.

"Climate models indicate sea surface temperatures in the central tropical Pacific are likely to rise further over the next few months, coming close to, or possibly exceeding, monthly values observed during the 1997–98 event," the Bureau of Meteorology said in its fortnightly update on Tuesday.

The years 2005, 2010 and 2014 have all been warmer than 1998 but 2015 is shaping up to be hotter yet. Since the effects of El Ninos tend to linger, climate experts are now pointing to 2016 as a possible rival for the next hottest year on record.

Australia's mean temperatures in August were 0.61 degrees above the 1961-1990 average, with cooler conditions in the country's south-east countered by unusually warm weather across northern regions.

The surging temperatures are likely to feature significantly in the run-up to the Paris climate summit in late November and December.

During El Nino years, less heat is taken up by the Pacific Ocean, typically adding 0.1 to 0.2 degrees to global surface temperatures.