The severe hot weather that hit northern and central regions over the last few days begins to drop slightly on July 6 although temperatures remain at highs of around 39 degree Celsius, according to the National Hydro-meteorological Forecast Centre.

The regions remain immersed in a heat wave with temperatures forecast to top nearly 41 degrees in Thanh Hoa, Nghe An and Ha Tinh provinces, according to the centre's deputy director Le Thanh Hai.

The heat wave is the most severe experienced in several decades.

The day-time temperatures on July 6 climbed to as high as 40-41 degrees while night-time temperatures hovered around 29-31 degrees.

In Hanoi, temperatures surged to 40.5 degrees July 6 and as high as 44-45 degrees on highways and public spaces while some provinces in the central region like Thanh Hoa and Nghe An recorded temperatures of between 40.4-41.5 degrees.

"High population density coupled with concrete roads and buildings and a large number of vehicles blocked breezes and contributed to pushing up temperatures in major cities such as Hanoi," said Hai.

He added that the hot spell was caused by a strong foehn wind in the low pressure area.

Foehn winds are caused by a rapid subsidence of moisture in the air after crossing mountain ranges, where moisture condenses, leaving a severe, dry wind, he explained.

"It is very hot and dry," he stressed.

In early June, the regions also suffered from a similar hot spell with temperature topping nearly 41degrees./.