National records were smashed in the scorching start to March, as the driest January-February in parts of northern Australia for half a century led to an unusual build-up of heat, according to the Bureau of Meteorology.

In a special climate statement on the heatwave that is yet to ebb in parts of south-eastern Australia, the bureau said the first three days of the month were each warmer than any previous March day, based on area-averaged temperatures across the nation.

Issac, 17, cools off at Parramatta Lake on Saturday. Credit:Brook Mitchell

The average maximum temperature of 38.14 degrees on March 2 broke the previous record for the month by 0.98 degrees – a margin that has only been surpassed once before, in July 1975, the bureau said.

A large high-pressure system became established in the Tasman Sea, directing hot northerly winds into inland parts of the country's south-east, setting up an exceptional, prolonged heatwave.