Buildings were barely visibly as a toxic haze shrouded northern Thailand.

Footage shows Chiang Mai city enveloped in heavy smoke that severely reduced visibility on April 7.

Swiss air quality company IQAir reported on April 7 that the air quality in Chiang Mai was at 265 AQI with a PM2.5 reading of 215 micrograms per cubic metre. The safe level in Thailand is 50.

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 powerful 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.