For the past two days Son La and Hoa Binh Provinces have been recording 40-41 degrees, temperatures usually only reached by mid-May.
Due to the impact of a low-pressure area in the west and Foehn winds, a type of dry, warm and downslope winds, several parts of the northwest became hot and sunny by March 31 with daytime temperatures reaching at least 35 degrees.
Nguyen Van Huong, head of the weather forecast department at the National Center for Hydro-Meteorological Forecasting, said hot weather has come around 1.5 months early to the north and a month early elsewhere.
Average temperatures across the country in March were 0.5-1.5 degrees higher than normal, he added.
Sixteen temperature records were broken in March, including the oldest one -- which had stood for 38 years -- in Dinh Lap, Lang Son, when, on March 5, the district recorded 36 degrees.
The center forecast April temperatures to be 1-2 degrees higher than normal.
Through the summer the number of warm days and temperatures would be higher than normal, it said.
More records are likely to be broken, it added.
Pham Thi Thanh Nga, head of the Institute of Hydrology and Meteorology Science and Climate Change, said the early arrival of summer heat is due to global warming, climate change and the El Nino effect.
Though El Nino will change to La Nina in the coming times, average temperatures in Vietnam would be higher than normal, she said.
"Quickly rising temperatures in certain places, lack of rain and droughts lasting months will increase the risk of forest fires."