The index on Sunday was 10, it said. An UV index reading of six or above means high risk of harm from unprotected sun exposure. A reading of 8-10 could cause skin burn after 25 minutes of exposure.

Nguyen Tien Thanh, deputy director of the laser and skin care department at the National Hospital of Dermatology in Hanoi, advised residents to use masks and thick fabric to prevent harm from sun exposure these days.

The use of SPF 50 sunscreen or more is advised for outdoor activities, he said.

The northern and central regions are forecast to record high temperatures during the next seven or eight days.

The mercury can go as as high as 38 degrees Celsius (100 degrees Fahrenheit) in Hanoi and 40 degrees Celsius (104 degrees Fahrenheit) in the north-central province of Nghe An.

Meanwhile, heavy rains, flash floods and landslides are expected next week in the northern mountainous region.