Footage shows buses belching out thick black clouds of fumes despite worsening air pollution in Bangkok.

The gas-guzzling ageing vehicles - many of them in service since the 1970s - are among the vehicles blamed for the toxic smog that clouds the city every year.

Officials have previously vowed to replace the fleet with environmentally friendly electric buses but the diesel engine vehicles are still on the roads.

Transport Minister Saksayam Chidchob said 12,500 electric buses were put on the roads last year and the government hopes to have up to 8,000 within three years.

Meanwhile, Bangkok Governor Chadchart Sittipunt said on January 5 that he spent 37 million baht to hire a private sector to operate a shuttle electric vehicle bus service for 21 months.

The 20-seat bus 'BMA Feeder' was operated by Electric Vehicles Thailand PLC.

Bangkok Metropolitan Administration prepared BMA Feeder buses for the 2022 Red Cross Fair on December 8 to 18.

During the Chinese New Year, BMA Feeder also transported passengers from Yaowarat road and Khao San road for free from January 20 to 23.

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.'