Data from Weather Online, a U.K.-based meteorological services provider, indicate the index in Ho Chi Minh City would climb to a 'very high' level of 10 on Saturday and 11 on Sunday, a dangerous level posing health risks to holiday-goers engaged in outdoor activities.

American forecast services provider AccuWeather said the city's UV would reach 9, also a "very high" level, on Saturday and 12 on Sunday.

The UV Index is an international standard measurement of the strength of ultraviolet radiation from the sun. Between 0 and 3 is considered low and above 11 is deemed extreme with radiation that could burn skin and damage eyes within 20-30 minutes.

Data from Weather Online also showed the UV index in Da Nang City in central Vietnam would rise to 11 this weekend while AccuWeather said it would reach 13 on Saturday and Sunday. The region has been battered by a severe heat wave over the past days.

Weather agencies forecast the UV index in Hanoi would reach 12 this Saturday but deem down to moderate levels on Sunday, thanks to a couple thunderstorms.

A heatwave began affecting northern, north-central, and central localities on Monday, raising the mercury across these regions to between 35 and 38 degrees Celsius, according to the National Center for Hydro-Meteorological Forecasting.

From Thursday until the weekend, the heat wave would continue hitting southern regions and the Central Highlands as well as south central provinces with temperatures reaching 35-37 degrees Celsius from noon to 3 p.m., it added.

Capital Hanoi braced as the temperature reached up to 35-37 degrees Celsius this week and is expected to stay there during the weekend, according to AccuWeather, which said real feel temperatures can reach 44 degrees Celsius on Saturday and drop to 42 degrees Celsius.

Weather Online said Hanoi's temperatures would reach 34-35 degrees Celsius this weekend while Vietnam's national forecast center said some places in the city can be affected by 40 degrees Celsius.

Statistics show since the beginning of the year, the average temperature across Vietnam reached 1 to 2.5 degrees Celsius higher than previous years, with the upward trend forecast to last till October.

Major heat waves are forecast to hit northern provinces in May and June, while scorching hot temperatures in north-central and central provinces will last till August.

Experts have advised residents to avoid direct exposure to sunlight between 10 a.m. and 3 p.m. and to wear sunscreen, sunglasses and brimmed hats if venturing out under the sun.

According to Le Thi Xuan Lan, a weather pundit based in southern Vietnam, a tropical depression is likely to form in the Pacific Ocean near the Philippines in early May, which will result in rain falling across multiple areas, including southern regions.

The rainy season is hoped to alleviate drought and saltwater intrusion that plaguing provinces in southern and central regions over the past months, Lan added.

Last year, Vietnam suffered a summer claimed to be the hottest in history with average temperatures 0.5-1 degrees Celsius higher than previous years, climbing to an average 39-42 degrees Celsius in many parts of the country. The nation broke its highest temperature record on April 20 as the mercury hit 43.4 degrees Celsius, or 110 degrees Fahrenheit, in Huong Khe District, Ha Tinh Province.