The weather bureau has confirmed a heatwave in the country's south-east last week and into the weekend smashed several hot weather records in South Australia, Victoria and Tasmania.

In a special climate statement, issued on Wednesday, the bureau said the most intense phase of the heatwave began building mid last week as a high pressure system in the Tasman Sea directed hot north-easterly winds inland, spreading extreme heat over much of the country's south-east on Friday and into the weekend.

The hottest temperatures were recorded in South Australia's Spencer Gulf on December 19, with Port Augusta reaching 47.2 degrees Celsius, Whyalla recording 45.8C and Port Pirie hitting 45.6C.

The temperature in the South Australian capital Adelaide, and surrounding areas, reached 40C every day from December 16 to December 19, marking the first time four consecutive days of 40C or above had been recorded in the city in December.

Victoria's highest temperatures were recorded in the state's west, with Avalon Airport, reaching 45C, while nearby Geelong recorded its hottest ever December day of 44C. Temperatures also exceeded 44C at a number of locations in the state's Wimmera region.

As well as numerous records being set for the hottest December daytime temperatures, there were also record high minimums, with areas of western Victoria and northern Tasmania enduring their hottest December night on record from Saturday evening into Sunday morning.

In Victoria's north-west, Mildura set a record for the state's hottest ever overnight temperature of 31.9C.