The drop in air quality across Bangkok over the past week is caused by an urban "dust dome" over the city.

The haze which has covered Bangkok over the past four to five days wasn't just caused by PM2.5 dust, as the amount of larger PM10 pollutants and greenhouse gases has also soared.

These pollutants, Natural Resources and Environment Minister Varawut Silpa-archa said, are the result of the burning of farming waste around the city's northern outskirts.

The minister said he has asked provincial governors to ask farmers in their area to avoid burning farm waste.

He also asked them to consider imposing a ban on outdoor burning if the farmers refuse to cooperate.

Schools will be allowed to delay their reopening if the haze problem in their area continues to deteriorate, he added.

He also encouraged Bangkok residents to avoid outdoor activities and keep their masks on while outside, to prevent health problems from PM2.5 as well as Covid-19.

PM2.5 levels in the capital were between 51-89 microgrammes per cubic metre (μg/m³); 69 areas in the city reported PM2.5 levels over the safe limit, which is set by the government at 50μg/m³.