From a high point on Mount Trebevic, which overlooks the city of Sarajevo in Bosnia and Herzegovina, a heavy layer of smog could be seen covering the entire city on Tuesday.

Bosnia and Herzegovina's capital has been covered in smog for several days. The air quality index measured by the US Embassy in Sarajevo hit 383 on Tuesday, a level identified by the World Health Organisation as hazardous to health and almost 10 times the average, making it one of the world's most polluted cities.

As winter arrives, the smog has intensified due to heavy traffic and the excessive use of coal, which many residents rely on to heat their homes because it is cheaper than electricity or gas.

"You can feel how bad the air smells even inside the car or home," taxi driver Mirsad Pobric told Reuters.