Electronics chain Dien May Xanh, which has 900 outlets in the country, says it sold 1,500 air purifiers last month, up 197 percent year-on-year.

"There is a rising demand for air purifiers as customers are concerned about their health. Some of our models are temporarily out of stock," a representative of the chain said.

Electronics chain Thien Hoa, with 17 outlets in HCMC, said that air purifier orders last month surged 140 percent over August.

Local stores have also reported high sales of air purifiers. Long, manager of an electronics store in HCMC’s Binh Thanh District, estimated that September air purifier sales doubled from August. "We sell 50-70 machines a day, and more customers are coming to ask questions every day."

Another store in HCMC’s District 3 said that they have only two machines left and customers have to wait for a few days for new stock.

In Hanoi, Electronic chain MediaMart, with 31 outlets in the city, reported sales of air purifiers in September surging by 245 percent from August.

Popular air purifiers in Vietnam are Japanese brands like Sharp, Daikin and Hitachi, South Korean ones like Coway, and Sweden’s Electrolux.

Prices vary between VND1.8-30 million ($78-1,297), with VND4-6 million ($173-259) the most popular range as machines in this range cover up to 40 square meters, enough for most homes.

Customers are also willing to pay for machines in the higher price range of VND7-12 million ($303-519), because these can reportedly filter out PM2.5 particulate, defined as superfine particles with 3 percent the diameter of a human hair.

The surge in demand for air purifiers comes as worsening air quality, manifest in Hanoi and Ho Chi Minh City in recent days as a thick haze, has become a matter of great worry for residents. At 9 a.m. Tuesday, Hanoi’s air quality index (AQI) was measured at 254, or "very unhealthy," while that of HCMC was 159, or "unhealthy."

Local stores in recent weeks have also recorded a surge in sales of masks, including that of high-end brands costing up to VND1.1 million ($47) each.