Authorities have issued a weather warning for most regions and called on citizens to avoid going out between 11am and 5pm.
However, for the thousands who work outside to make a living, staying indoors or working in the shade is not an option.
The mean temperature across the country will hover between 40°C and 44°C but is expected to reach a high of 48°C in the south-west.
It is expected to be slightly cooler in coastal areas and in high lands, between 36°C and 40°C.
Wildfires broke out on Tuesday afternoon in the mountainous area of Maloula Tabarka in the north-west as a result of the heat.
Every day, Naouefl Mekni, 42, leaves his home in Raoued at 7am and returns home at night. He collects plastic for a living, a job that a growing number of struggling Tunisians are taking on as work opportunities become more scarce.
“I do this every day and I can barely manage to survive,” Mr Mekni told The National as he took a brief moment to rest and drink water.
“I need to bear with this heat and the probability of getting ill to make a living for my children."
Mr Mekni, a father of two children aged five and six, said he needs to collect at least 40kg of plastic a day to earn enough to feed his family.
His job becomes harder in excessive heat.
Wissem is painting newly built apartments at construction sites in Soukra. He told The National he would simply lose his job if he stayed home because of the heat.
“There is no way they [his employers] would change our working hours or find any other alternative, they do not care about us, even if you’re sick you have to come and work,” he said.
“Whether it gets hot or cold, you have to work otherwise you can’t get paid."
At another construction site in L’Aouina, workers echoed Wissem’s complaints.
“Whether we work during the day or at night, it’s the same,” Wssaief Ouji, 59, told The National as he rested in the shade under a concrete mixer.
Saiden Ltifi, 58, who works on the same construction site, said most people could not stand in such heat for a few minutes, let alone work in it for the entire day.
“We just have to finish our job within a specific time, some people have deadlines others need to make a living day by day, that is just our reality,” he said.
“Whether it gets hot or not, we cannot do anything, that is the life of a construction worker, we struggle either way.”
Despite the challenges, Mr Ltifi takes great pride in his work.
“Our life is a big hardship but we have to bear with it for our children’s livelihood,” he explained.
“Despite the pressure of this lifestyle, it remains better than stealing or begging … it’s a job one must do with lots of honour.”
Some workers on site wear several layers of clothes, hats and towels to protect themselves from sunburn and heat stroke.
“We try to fight it by drinking lots of water, wearing hats and extra layers of clothes,” Mr Ltifi said.
But workers' energy levels are severely affected by the heat, they say.
“We feel tired very easily these days,” Sabeur, 35, told The National.
“This is the toughest job in the world, who would be able to bear to work under this scorching sun for eight hours straight?” he said.
Sabeur said working outdoors in the extreme heat felt like a hard labour prison sentence.
In summer, many Tunisians eat watermelon to stay hydrated and fight the scorching heat. But for those who make a living selling them, staying cool and hydrated is not so easy.
“We spend days on the road from one field to the other across Tunisia to be able to secure our merchandise and bring it back to Tunis,” Saifeddine Rahmani, 28, told The National in Soukra Tunis.
He said he usually heads out at 7pm, taking hours to reach the farms where he and others obtain their stock, a journey he said was especially difficult in the intense heat.
“The heat on the road is even more unbearable, sometimes we would not even find the shade of trees to take cover, so we have to lay under our trucks to rest,” he said.