Kuching (Malaysia), Hanoi, Kuala Lumpur, Jakarta and Singapore topped the list of major cities with the highest air pollution levels in the world according to Air Visual, a platform that measures the Air Quality Index (AQI) worldwide.
However, the highest levels of air pollution were recorded in rural areas, reports Efe news.
Simpang, in Indonesia's Sumatra island, surged to the "Hazardous" category of 372 on the AQI, with the density of PM2.5 particles at 322.6 micrograms per cubic meter.
PM2.5 are harmful ultrafine particles that measure 2.5 micrograms or less in diameter. The World Health Organization recommends that levels should not exceed 25 micrograms per cubic meter.
Sri Aman on the Malaysian part of the Borneo Island, stood at 367 on the AQI and recorded PM2.5 levels of 317.2 micrograms per cubic meter.
AQI levels of 151 and above are considered unhealthy, especially for children, the elderly and the sick; it is advisable to stay indoors once they are reached.
Most of the smoke affecting Indonesia, Malaysia and Singapore billowed from forest fires and plantations on Indonesian territory, mainly in Sumatra and Borneo.
More than 2,000 people have received medical treatment in Kalimantan, in Indonesian Borneo, for respiratory problems due to smoke inhalation. Indonesian authorities arrested more than 180 people on Monday and were investigating more than 30 companies - some in the palm oil industry - for their possible role in the fires.
The blaze began at the beginning of the country's dry season in June, and more than 9,000 firefighters and volunteers have since worked to extinguish it.
Indonesian media reported that two people had died - including a baby - from inhaling the toxic fumes rising from the fire that has ravaged Sumatra in recent weeks.
In Malaysia, the Education Ministry has ordered the closure of 138 schools in Selangor state this week and another 56 in Port Dickson due to the poor air quality.
Hanoi has been witnessing alarming levels of smog mainly due to pollution from nearby coal plants and road traffic.
( With inputs from IANS )