According to the National Centre for Hydro-Meteorological Forecasting, the heatwave would initially affect the area from Thanh Hoa to Danang, along with eastern parts of the central highlands, including Quang Ngai and Dak Lak provinces.
Daytime temperatures in these areas are expected to range between 35 and 38 degrees Celsius, with some locations exceeding 39 degrees.
From May 23, the heatwave is forecast to expand across northern Vietnam, where temperatures could reach 35-37 degrees Celsius and rise above 38 degrees in isolated areas.
Meteorologists warned that prolonged hot and dry conditions could increase the risk of fires and explosions in residential areas due to rising electricity demand.
Health experts advised people to avoid outdoor activities during the hottest hours of the day, typically between 10 am and 4 pm, while staying hydrated and limiting prolonged exposure to extreme heat.
Authorities also urged extra precautions for vulnerable groups including children, the elderly and people with underlying medical conditions.