The National Center for Hydro-Meteorological Forecasting revealed the northern region had recorded 21 sweltering days in June with average temperatures 1.5-2.5 degrees Celsius higher than previous years. This is considered the longest heat wave to hit the region since 1971.

Temperatures in northern provinces like Lang Son, Bac Ninh, Bac Giang, Hai Duong, Hung Yen, Ha Nam and Ninh Binh were recorded at 36-39 degrees Celsius last month while Hanoi's Ha Dong District monitoring station reported 26 consecutive hot days during the month.

The heat wave was caused by low-pressure areas from the west and the Foehn wind, a type of dry, warm and down-sloping wind that occurs in the lee of a mountain range, said Nguyen Van Huong, head of the center's weather forecasting department.

The central region also recorded 27 hot days, with temperatures ranging mostly from 36-39 degrees Celsius. Do Luong District in central Nghe An Province reported its highest temperature at 41.2 degrees Celsius, followed by Huong Khe District in neighboring Ha Tinh Province at 41.1 degrees Celsius.

Hot weather has caused acute shortage of irrigation water across the provinces, as well as a series of forest fires.

Vietnam has experienced scorching days since early May.

On May 21, the temperature in Hanoi's Ha Dong District peaked at 40.9 degrees Celsius, the highest May temperature since 1961. On the same day, parts of Lao Cai, Hoa Binh and Ha Giang also recorded their highest May temperatures in decades.

Last year, Vietnam went through possibly the hottest summer in history with average temperatures 0.5-1 degrees Celsius higher than previously, climbing to an average 39-42 degrees Celsius in many parts of the country. The nation broke its temperature record on April 20, 2019 as the mercury hit 43.4 degrees Celsius, or 110 degrees Fahrenheit, in Huong Khe District, Ha Tinh.

According to the Intergovernmental Panel on Climate Change, Vietnam is expected to lose 5.7 percent of its GDP to excessive heat by 2030, with unprecedented temperatures costing it $85 billion in productivity loss, as the climate makes outdoor work near impossible in the summer months.