The resulting drought has brought an "unprecedented natural disaster," said the isolated nation already grappling with tough international sanctions over its nuclear weapons programme.
It has warned against crop damage that could savage its farm-reliant economy, battered by sanctions despite recent diplomatic overtures.
"This high-temperature phenomenon is the largest, unprecedented natural disaster, but not an obstacle we cannot overcome," the North's Rodong Sinmun said, urging that "all capabilities" be mobilised to fight the extended dry spell.
Temperatures have topped a record 40°C (104°F) in some regions since late July, and crops such as rice and maize have begun to show signs of damage, the mouthpiece of the ruling Workers' Party said in a front-page commentary.
"Whether the current good crop conditions, for which the whole nation has made unsparing investment and sweated until now, will lead to a bumper year in the autumn hinges on how we overcome the heat and drought," it added.
Similar past warnings in state media have served to drum up foreign assistance and boost domestic unity.
"I think the message was a precautionary one to minimise any impact on daily life," said Dong Yong-seung, who runs Good Farmers, a group based in Seoul, capital of neighbouring South Korea, that explores farm projects with the North.
But the mention of unprecedented weather, and a series of related articles, suggest the heat wave could further strain its capacity to respond to natural disasters, said Kim Young-hee, a defector from North Korea and an expert on its economy at Korea Finance Corp in Seoul.
The warning comes after North Korean leader Kim Jong Un announced in April a shift in focus from nuclear programmes to the economy, and held an unprecedented June summit with U.S. President Donald Trump in Singapore.
Since then, the young leader has toured industrial facilities and special economic zones near the North's border with China, a move experts saw as a bid to spur economic development nationwide.
"He has been highlighting his people-loving image and priority on the economy but the reality is he doesn't have the institutions to take a proper response to heat, other than opening underground shelters," added Kim, the economist.
Good crop conditions
Drought and floods have long been a seasonal threat in North Korea, which lacks irrigation systems and other infrastructure to ward off natural disasters.
Last year, the U.N. Food and Agriculture Organisation warned of the North's worst drought in 16 years, but late summer rains and privately produced crops helped avert acute shortages.
There appear to be no immediate signs of major suffering in the North, with rice prices stable around 62 U.S. cents per kg through the year to Tuesday, a Reuters analysis of data compiled by the Daily NK website showed.
The website is run by defectors who gather prices through telephone calls to traders in the North, gaining a rare glimpse into the lives of ordinary citizens.
Crops are good this year because there was little flooding to disrupt the early spring planting season, said Kang Mi-jin of the Daily NK, based in Seoul.
"They say nothing remains where water flowed away, but there is something to harvest after the heat," Kang said, citing defectors. "Market prices are mainly determined by Chinese supplies and private produce, rather than crop conditions."
The October harvest would reveal any havoc wreaked by the weather, Kim Young-hee added.
North Korea suffered a crippling famine in the 1990s when a combination of bad weather, economic mismanagement and the demise of fuel subsidies from the Soviet Union all but destroyed its state rationing system.
However, rationing has slowly been overtaken by an increase in foreign products, mainly from China, and privately produced food sold in North Korean markets, a factor experts say U.N. reports overlook.
The neighbours are in talks to help the North modernise its economy, step up disaster response measures and expand forests in a follow-up to April's historic summit between Kim and South Korea's President Moon Jae-in.
Across the border, temperatures hit 39.6°C (103.28°F) in Seoul on Wednesday, their highest since weather authorities began monitoring in 1907. The heat has caused 29 deaths and injuries to more than 2,350 people, health officials have said.