· Moron’s guide to dealing with heatwaves
· What defines a heatwave

Power may be cut from 100,000 Victorian homes and businesses as the state struggles through a severe heatwave which is now extending across much of New South Wales as well as South Australia and Tasmania.

The mercury peaked at more than 40 degrees throughout much of Victoria on Wednesday, the second day of an extended hot spell tipped to continue until Friday night.

Charlton, in the state’s northwest, was the hottest place in Victoria, reaching a scorching maximum of 46.2C.

Victorian Energy and Resources minister Nicholas Kotsiras said forced blackouts were possible as the high temperatures put the national electricity network under serious strain.

The Australian Energy Market Operator (AEMO) was considering reducing the supply to Victoria, with the potential to affect 100,000 homes and businesses.

A statement from AEMO said Victoria and South Australia had this week recorded their highest demand for electricity since 2009.

The Bureau of Meteorology issued a severe thunderstorm warning for much of the southern half of Victoria, with damaging wind and possible hail predicted for Melbourne, Ballarat, Geelong, Traralgon, Bairnsdale and Orbost on Wednesday evening.

But the storms aren’t likely to cool Victorians down, with Melbourne set to reach 44C on Thursday and 42C on Friday, before a southerly change comes through.

Ambulance crews on Tuesday and Wednesday responded to dozens of cases of heat stroke and a larger than usual number of heart attacks.

Ambulance Victoria operations manager Paul Holman said there were 11 children left in cars on Tuesday, and five had to be freed from cars on Wednesday.

At least nine people suffered cardiac arrest and 62 people needed treatment for heat stress on Wednesday, Ambulance Victoria said.

Among the cases of heat stress in recent days were people collapsing while exercising outdoors, including joggers and people on golf courses and bowling greens.

If the temperature passes 40C in Melbourne on Thursday and Friday, it will be the first time the city has endured such a heatwave since 1908, when there was a five-day streak above 40C.

Bushfire conditions

Dangerous bushfire conditions are expected to continue, with a total fire ban declared for the state on Thursday and a similar declaration likely on Friday.

However the state’s top firefighter says conditions are unlikely to reach the catastrophic levels of Black Saturday, despite reports of 15 uncontained fires burning on Wednesday afternoon and authorities warning residents of severe fire danger for Friday.

Fire Services Commissioner Craig Lapsley said the fire danger, while serious, was not the same as February 7, 2009, when 173 people were killed and more than 2000 homes were destroyed.

“The whole day is not as severe – that’s not to say we won’t have fires and we won’t have fires that do damage,” Mr Lapsley told reporters.

“But it’s not the same forecast. It’s a severe day, not a code-red day and there is a difference.”

Heat and fires in South Australia

The hot weather is also continuing in Adelaide, with the temperature hitting 43.2C at 1.30pm (ACDT) today.

Temperatures hit 44.3C at Roseworthy, north of Adelaide and in Port Augusta.

It could get even hotter over the next couple of days with 46C temperatures forecast on Thursday, and 40C the forecast for Friday.

After 45-degree-plus temperatures yesterday, residents near Paringa in SA saw this lightning storm #heatwave pic.twitter.com/bAJIFsIUgB

— ABC News (@abcnews) January 15, 2014

The city’s record maximum is 46.1, recorded in January 1939.

Several fires are burning across the state with conditions set to possibly worsen as temperatures again climb into the mid-40s.

More than 300 Country Fire Service (CFS) crews have fought scores of fires in the state, many started by lightning strikes.

A woman was taken to hospital after she was burnt trying to defend her home from a fire at Rockleigh, south-east of Adelaide.

“The house just caught (fire) while she was in there and her husband came running to the rescue and ripped her out while she was trying to grab some small animals,” the woman’s brother Mark Hansen said.

Photo gallery: See how Australians (including this Jack Russell) are coping with the #heatwave http://t.co/FwrCDqlcjJ pic.twitter.com/LRQJAhxLe3

— ABC News (@abcnews) January 15, 2014

About 100 firefighters are still battling the blaze at Rockleigh, which has burnt through more than 4,500 hectares.

The CFS is also battling fires on Lower Eyre Peninsula, and in the Barossa and Clare Valleys.

Severe fire danger ratings have been issued across the state.

Heat to hit Sydney and New South Wales

Sydneysiders will experience higher air pollution and workers will risk being struck down with heat stroke as the heatwave sets in across NSW.

High temperatures plagued parts of the state including western Sydney on Wednesday as coastal communities were largely spared the swelter.

Penrith reached 39.2 degrees Celsius in the afternoon while Horlsey Park hit 37C.

But country towns bore the brunt of the heat.

Deniliquin in the Riverina reached 44C and Ivanhoe in the central west climbed to 43C.

Similar conditions forecast for Thursday have prompted a warning from NSW Health, citing concerns pollution from car exhausts and industrial fumes get worse on hot and still days.

Professor Wayne Smith of New South Wales Health urged parents to plan outdoor play in the morning when ozone levels were lower.

“Ozone can also irritate the lungs of healthy adults, so it is best to avoid any prolonged outdoor exercise,” he said.

WorkCover NSW has alerted outdoor workers to the symptoms – nausea, dizziness and collapse – of heat-related illness.

It says rotating tasks to lessen sun exposure and working at cooler times of the day can reduce risks.

Tasmania prepares for fire danger