Footage shows haze blanketing Bangkok this morning as the country enters its annual 'pollution season'.

The toxic smog comprised of harmful PM 2.5 particles appears annually when crop burning increases and atmospheric conditions become calmer, with less wind and rain.

Authorities have failed to tackle the chronic problem - blamed for rising cases of respiratory conditions - for several years.

In some parts of the city, the level reached more than 150 on the Air Quality Index (AQI), more than triple the safe level of 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. This is combined with high numbers of polluting cars on the road and large construction projects across the capital.

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 – prevent the pollution from being dispersed naturally.

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.'