The fires killed at least 34 people, including 10 soldiers, as they raged through residential areas, the interior ministry said, revising an earlier toll of 15 dead.
According to that initial toll, at least 26 people were also injured.
Some 1,500 people were evacuated from the Bejaia, Bouira and Jijel provinces east of the capital Algiers, according to the ministry.
The three provinces in Algeria's Mediterranean coastal region have seen the worst of the fires.
President Abdelmadjid Tebboune on Monday expressed his condolences to the families of the deceased.
The interior ministry said that 7,500 firefighters and 350 firetrucks were mobilised with aerial support to fight the flames.
Operations were underway to extinguish fires in six provinces, it added, calling on citizens to "avoid areas affected by the fires" and to report new blazes on toll-free phone numbers.
"Civil protection services remain mobilised until the fires are completely extinguished," the ministry said.
The Bejaia prosecutor's office has ordered a preliminary probe to identify the causes of the blazes and potential perpetrators, it said in a statement.
Images shared by local media showed fields and forests that had caught fire in the area as well as charred vehicles and storefronts destroyed by the flames.
In the northeastern province of Tizi Ouzou, 15 fires were extinguished late Sunday, according to civil protection forces.
Fires regularly rage through forests and fields in Algeria in summer, and this year have been exacerbated by a heatwave that has seen several Mediterranean countries break temperature records.
Mediterranean heatwave
In neighbouring Tunisia, temperatures on Monday neared 50 degrees Celsius.
Tunisia's state energy supplier STEG announced planned half-hour to one-hour power cuts in a bid to preserve the network's performance.
Fires raged again on Monday in a Tunisian pine forest near the border with Algeria, after another blaze in the area last week.
At least 300 people were evacuated by sea and by land from the village of Melloula, according to the national guard.
AFP journalists saw extensive damage near the town of Nefza, about 150 kilometres (90 miles) west of Tunis.
During last week's fire, a border crossing had to close temporarily, according to Tunisian officials who confirmed 470 hectares (1,100 acres) of forest had been burned.
In some other North African countries such as Morocco and Libya, temperatures were relatively normal compared to annual averages.
Algeria's state energy firm Sonelgaz on Sunday reported a peak in electricity consumption at 18,697 megawatts.
In August 2022, massive blazes killed 37 in Algeria's northeastern El Tarf province.
It was preceded by the deadliest summer in decades, with 90 people killed in such fires in 2021, particularly in the Kabylie region.
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