Forest fires continue to ravage northern Thailand this morning, with air pollution levels making the region the worst in the world.

The wildfires broke out at the Doi Saket district of Chiang Mai province on April 4, prompting authorities to dispatch helicopters to aid firefighters.

Kritsayam Kongsatri, the director of the Protected Area Regional Office 16 in Chiang Mai, said on April 5 that the blaze had successfully been controlled at 12:30 AM, with recon teams monitoring the area for reignitions.

A new 'hotspot' had also been reported in Ban Huai Sai village in the Mae Rim district. The Ministry of Natural Resources and Environment said it would send helicopters to survey the area before a ground firefighting team was deployed.

Meanwhile, emergency services are still battling fires in the Srilanna National Park and the Chiang Dao district.

Swiss air quality company IQAir reported today that Chiang Mai had an air quality level of 290 with harmful PM2.5 particles in the air reaching to 178.2 grams per cubic metre - more than 35 times the safe level from the World Health Organisation.

Chiang Mai and Chiang Rai - two of the country's most popular city destinations - have been enveloped in a toxic haze for several months, with business owners and residents now urging the local government to declare the district a 'disaster area'.

The designation would allow resources to be mobilised quickly to address the hazardous PM2.5 dust levels, which have been responsible for thousands of hospital admissions.

However, defiant Chiang Rai governor Puttipong Sirimat and Interior Minister Anupong Paochinda refused to address the 'disaster zone' issue, fearing the 'negative impact' of the label on tourism.

Interior Minister Anupong added there was no clear PM2.5 dust threshold to declare a disaster because the pollution levels change constantly.

Scientists found that smog is at its worst in the country when farmers burn waste crops to cheaply clear their land between late October and April. It has been worsened in recent years by rising demand for food and agro-business lobbyists that can stifle the government's control over farmers.

The seasonal lack of wind and rain, combined with a winter low-pressure system in which cold air is trapped closer to the ground by warm air above – hampers the pollution from being dispersed naturally by wind.

The Thai government has been criticised for failing to tackle the country's air pollution crisis, with bizarre measures such as spraying water into the air and giant purifiers having no impact.

Data scientist engineer Worasom Kundhikanjana said: 'PM 2.5 pollution has a seasonal trend in Bangkok and the northern provinces, but has only recently received public attention. During this winter haze, the harmful particle pollution level is high throughout the day, including on weekends.

'Unfortunately, spraying water into the air does not appear to be effective, since the volume of water is minuscule compared to actual rain.

'With the start of the monsoon season, the weather in Bangkok will get better, and public attention on this issue will likely fade. However, without immediate policy measures, the problem will come back again next winter.'