Australia has posted two of its hottest days on record this week. The average maximum temperature across the country reached 40.33°C on Monday, beating the previous record of 40.17°C set in 1972, the Bureau of Meteorology's Dr David Jones said.
Yesterday temperatures were expected to reach 43°C in Sydney and 45°C elsewhere in New South Wales.
Average maximum temperatures have risen above 40°C only three times in recorded history.
"We had the hottest day on record for Australia and (yesterday) it looks like we may well go better again," Jones said.
"This really puts the national dimension of this heat event into bigger context."
Other data from the bureau showed maximum temperatures across the continent in the last four months of 2012 were 1.6°C above average, breaking all previous records.
Aaron Coutts-Smith, the bureau's NSW manager for climate services, expects the dry and hot conditions to continue for at least the next week. "What makes this event quite exceptional is how widespread and intense it's been. We have been breaking records across all states and territories in Australia over the course of the event so far."
Hobart recorded its hottest day in 120 years on Friday, when the temperature peaked at 41.8°C.
Hay, in southwest NSW, climbed to 47.7°C on Saturday - its highest in 56 years.
Sydney was expected to reach a maximum of 43°C yesterday, which would make it the third-highest temperature on record.
Dr Markus Donat, from the Climate Change Research Centre at the University of New South Wales, says periods of high temperatures have increased. "In recent studies we have analysed how extreme temperatures have changed globally. For most regions, including Australia, we found that extremely high temperatures have become more frequent and more intense."
Donat's research also shows extremely low temperatures have occurred less frequently than they did in the middle of the 20th century.
"Counting the number of very warm days (defined as the warmest 5 per cent between 1951 and 1980) we found that during the most recent three decades ... the frequency of days in this warmest category has increased by 40 per cent globally," he said.
Heatwave conditions engulfed NSW with temperatures exceeding 30°C soon after sunrise yesterday.
Bega, on the NSW south coast, was the first town to hit 40C at 11.30am.
It recorded 37.8°C at 9am after temperatures rose almost 15°C in an hour, up from from 23°C at 8am. After a southerly wind change just after 2pm temperatures eased to the mid-20s.
Temperatures of 40°C were recorded in Sydney at 12.30pm, up from 27°C at 9am.
Many yesterday stayed indoors, while the more adventurous headed to the beach.
While workers can luxuriate in air-conditioned offices, holidaymakers were finding other ways to cool down.
Extra surf lifesavers volunteered yesterday at beaches that are not normally patrolled on weekdays.
Surf Life Saving NSW lifesaving manager Dean Storey said lifesavers were aware temperatures would be as high as 30°C late at night and into this morning.
"They've been planning especially for an increase in potential activity after hours. We'd urge people to plan their swim for patrol hours."
Moviegoers took advantage of "cheap Tuesday" ticket prices to catch new releases. Some Event and Greater Union cinemas in suburban areas had eclipsed their Boxing Day sales by 11.30am yesterday. "It's a rather big day," a cinema spokeswoman said.
Child Care NSW president Vicki Skoulogenis said centres were likely to restrict children from going outside.
"(We will be) making sure that the children are not exposed to any direct heat from external sources, such as going out on verandas or out in a playground."
She advised parents with children at home to take similar precautions, or take them somewhere cool. "Dare I say, the shopping centre," Skoulogenis said.
Train passengers were warned to travel with water and notify staff if they feel unwell.
At busy stations, staff handed out bottled water and misting fans were in operation at some platforms at Sydney CBD stations.
About 76 per cent of CityRail trains and about 87 per cent of Sydney buses are airconditioned.
The ACT Ambulance Service said it had treated 19 people for heat-related illnesses even though the thermometer in Canberra didn't peak as high as other cities with a maximum of 38°C. "Keeping cool and hydrated is key to staying safe and healthy during hot summer days," the ACT Emergency Services Agency said.