A MAN has been arrested over a blaze on the outskirts of Melbourne, while hundreds of people have been hospitalised for heat stress in South Australia, as the country battles through a dangerously hot weekend.

Total fire bans are in place this weekend for Tasmania, large areas of SA and Victoria, while high temperatures in New South Wales have firefighters on alert.

Thousands of rural and metropolitan firefighters have been placed on the highest state of alert.

The SA heatwave has already put hundreds in hospital, including an apprentice carpenter who was in a critical condition after collapsing while working in extreme heat in Adelaide.

Here we break down what’s happening around the country.

VICTORIA

As temperatures hit at least 40 degrees in many parts of Victoria, firefighters have been battling three fires.

Ambulance Victoria says its officers had been called out to four cases of children locked in hot cars, none of whom needed emergency care.

They said having the car running with the air conditioning is “no excuse” and it is potentially lethal, as well as subject to heavy penalties.

The service said paramedics had attended a higher-than-usual number of cardiac arrest, heart problems and chest pain cases.

There had been 22 cases directly attributable to the weather, including heat exposure and kids in hot cars.

Victoria Police said a man has been arrested over a blaze on the northern outskirts of Melbourne, which caused the closure of the Hume Freeway at Epping.

The fire, which is now detained, started just after 10am as the local temperature hit 36 degrees.

The 34-year-old man, of no fixed address, was arrested in Vearings Road at about 12.50pm and is being questioned.

More pics from #Epping fire. Traffic was dangerously close to the fire @7NewsMelbourne pic.twitter.com/I2qz2JXYMf — Shayne Whiteley (@7newspilot) December 19, 2015

Meanwhile, homeowners, neighbours and firefighters scrambled to save houses from a rapidly growing grass fire in Wonthaggi in the Gippsland region.

The Country Fire Authority issued an emergency warning for Wonthaggi, Harmers Haven and Cape Paterson.

The blaze started just before 1pm as a small grass fire on the edge of the town just metres from homes and quickly grew as it moved into an area of thick scrub and bushland, the Herald Sun reports.

Flames leaping up to 30m high threatened the area as homeowners and their neighbours rallied behind CFA crews in a brave bid to stop the blaze reaching nearby houses in Shandley Street and Bell Lane.

A separate grassfire burning at the foothills of Victoria’s Dandenong Ranges has now been contained. The CFA has downgraded its warning to ”watch and act” for Wandin North.

“While the immediate threat has passed, continue to stay informed and monitor conditions,” the CFA says.

Wandin North resident Brenny Cullen watched on as numerous waterbombers fought the fire just 500 metres from his home.

“There is a lot of smoke, it’s a grass fire but lots of firefighters are around,” he told AAP.

Nicole Williams was visiting friends in Wandin North when she was told to leave because the fire was at the end of the street.

“The smoke hadn’t blown over when I was there but there was a huge plume,” she said.

“The colour of the air turned orange just before I left.”

A total fire ban has been declared for Sunday with Melbourne expecting a record minimum temperature of 30C on Saturday night.

A severe thunderstorm warning has been issued for parts of western and central Victoria.

Severe thunderstorm warning issued for parts of western and central #Victoria for damaging wind gusts. Details: https://t.co/PNs0WBVDhw — BOM Victoria (@BOM_Vic) December 19, 2015

As Melburnians swelter, Victoria’s union chiefs are engaged in a dispute with officials.

Acting chief officer at the Metropolitan Fire Brigade, David Bruce urged firefighters on Thursday to make themselves available over the weekend and update their availability on the firefighter recall system, the Herald Sun reports. His plea came after one in three MFB firefighters called in sick last Saturday night.

The newspaper said the United Firefighters Union told their members to ignore the plea because they weren’t consulted before the request was made, but union secretary Peter Marshall denies the union did that.

“Firefighters will be rostered as usual 24/7 across all MFB stations this weekend,” he said in a statement today.

“As usual they will be available for recall or to form strike teams if they are needed.”

A large number of firefighters called in sick last weekend, following the suicide of two colleagues within 72 hours from the same fire station, Mr Marshall said.

“Firefighters suffer extraordinary levels of post traumatic stress disorder and much of their work is dangerous, dirty and confronting,” he said.

“The sudden loss of two friends recently had a huge impact on the firefighting community.”

The extreme fire season that’s been predicted will also add to an already challenging job, he said.

SOUTH AUSTRALIA

In SA, the risk of bushfires is also increasing as winds rise ahead of a cool change set to sweep across the state late tonight and into Sunday morning. The blistering conditions have been blamed on a stationary high pressure system in the Tasman Sea, which has been dragging hot air from the centre of Australia.

SA’s heatwave, where the mercury has passed 40 degrees on each of the past three days, left apprentice carpenter Travis Mellor fighting for his life after he collapsed on a building site on Wednesday. The 17-year-old has regained consciousness after slipping into a coma for several days.

He was one of more than 100 hospital admissions over the past three days for heat-related issues with that number set to rise once today’s figures are included.

The severe heat has also forced Thoroughbred Racing SA to cancel a scheduled race meeting at Morphettville Racecourse in Adelaide today.

Wildlife and conservation parks on the Eyre Peninsula will also be closed.

NEW SOUTH WALES

In NSW fighterfighters also remain on high alert as the mercury rises. At least 32 fires are burning across the state, with five of those classified as out-of-control.

“The good news is that none of those are posing any threat to properties,” Inspector Ben Shepherd from the NSW Rural Fire Service said today.

He said firefighters were particularly monitoring a large bushfire near the NSW-ACT border which has been burning since Wednesday night.

Severe weather conditions forecast for tomorrow could cause the fire at Mount Clear to spread to areas of NSW between Michelago and Bredbo, he said.

No total fire bans are in place today but there is still a high fire danger.

Mr Shepherd urged people to use the day to make sure their fire plans are in place as temperatures are predicted to soar tomorrow.

“As much as it’s a beautiful weekend, please go out and do your house work before you enjoy the day,” he said.

Total fire bans are likely to be put in place tomorrow and the RFS will provide an update this afternoon, he said.

TASMANIA

A total fire ban is in place across most of Tasmania for the weekend with temperatures forecast to reach well past 30 degrees. North and south regions will be subject to high or severe-risk fire danger levels, flamed by dry conditions and strong winds. Fire crews are on standby and will be deployed to hot spots pre-emptively, authorities said.

WESTERN AUSTRALIA

In contrast, Perth is experiencing a mild weekend with a maximum of 24 degrees forecast for today and a high of 29 on Sunday. However, bushfire warnings remain in place across WA, with a severe threat for parts of the Pilbara.

The DFES this morning issued a severe fire danger rating for inland parts of west Pilbara, including the Shire of Ashburton, due to a change in weather conditions.

“These are very hot, dry and windy conditions for a bush or grass fire,” the warning said

Nearby residents have been urged to prepare for the imminent threat of a fire.

“If a fire starts and takes hold, it will be unpredictable, move very fast and (be) difficult for firefighters to bring under control,” DFES said.

Meanwhile, a bushfire alert remained in place for people travelling on the Great Northern Highway between Kumarina Roadhouse and Three Rivers Station in the Shire of Meekatharra.

The out-of-control bushfire wasn’t threatening homes, but it was causing a lot of smoke in the area, the department said.

Another out-of-control fire was burning in the western part of Bullsbrook in the City of Swan.

It wasn’t threatening homes either, but had created a lot of smoke.

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