A score of between 101 and 200 qualifies as unhealthy, with Johan Setia Klang (189), Banting (166), Petaling Jaya (137) and Klang (117) breaching this threshold as at 1pm today.

Elsewhere in the country, Rompin, Pahang, also registered unhealthy air quality with a reading of 129.

According to API’s hourly reports, the worsening of air quality began overnight, with Banting first recording unhealthy levels at 11pm, while the rest occurred in the early hours of the morning.

There has been no official word on the causes of the reduction in air quality.

According to the Asean Specialised Meteorological Centre, pollution has been detected across the region.

“Isolated hotspots were detected in Myanmar, Thailand as well as in Peninsular Malaysia and Sumatra. Most air quality stations over the central Mekong sub-region reported moderate to unhealthy values,” it said this morning.

“Several stations in the eastern parts and northern highland regions of Thailand reported very unhealthy air quality values.”

Yesterday, environment and water minister Tuan Ibrahim Tuan Man said in a Facebook post authorities were investigating a fire on a private land in Pontian and advised against open burning activities given the current hot and dry conditions.

“Open burning is an offence under Section 29A of the Environmental Quality Act 1974, which is punishable by a RM2,000 compound, a fine of up to RM500,000 or a prison term not exceeding five years, or both,” he said.