Health bodies are urging people to drink plenty of water and stay out of the heat. 

The Bureau of Meteorology's acting regional director in South Australia, John Nairn, says while heatwaves are a normal part of the Australian summer, the current blast is unusual for the large area it is covering. 

``More than 70 per cent of the continent is currently experiencing heatwave conditions,'' he said. 

``Severe heatwave conditions across the interior of Australia are set to continue for a while yet.'' 

Among the hottest parts of the country yesterday were Wudinna, on South Australia's Eyre Peninsula, which hit 48.2 degrees, Adelaide reached 45 degrees and Hobart.

The Bureau of Meteorology says the scorching heat bearing down across many states will continue ``unabated'' well into next week. 

The National Heart Foundation is advising those with heart disease to take it easy during the next few days, with studies showing an increase in heart attacks and death from extreme heat. 

The foundation says people most at risk are those with a chronic disease, such as heart disease, and the elderly, children, people on certain medications and those engaged in strenuous outdoor activity. 

Police have also warned that leaving children, elderly people or pets unattended in cars could prove fatal in hot weather. 

Surf lifesavers are expecting to have to rescue hundreds of beachgoers this weekend as swimmers escape the heatwave in NSW. 

Prime Minister Julia Gillard has called on people to be careful.