Indonesia has deployed nearly 21,000 personnel to fight forest fires raging in its northern islands, as thick smoke cloaks much of the region. Hazardous smog has blanketed parts of northern Indonesia, Singapore and Malaysia.

South-east Asia has suffered for years from annual bouts of smog caused by slash-and-burn practices on Sumatra and Kalimantan islands, and the fires have been exacerbated this year by the effects of the El Nino weather phenomenon, as a prolonged dry season has parched the soil, fuelling the flames.

These interactive before-and-after photos show how visibility in neighbouring Singapore has been dramatically affected.

Indonesia fire Singapore smoke haze
Indonesia fire Singapore smoke haze
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People relax in an infinity pool overlooking the skyline of the central business district of Singapore on 14 September and 10 July 2015          (Edgar Su/Reuters)
Indonesia fire Singapore smoke haze
Indonesia fire Singapore smoke haze
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Vehicles travel on the causeway from Singapore to to Malaysia on 29 September 2015 and 5 May 2015          (Edgar Su/Reuters)
Indonesia fire Singapore smoke haze
Indonesia fire Singapore smoke haze
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People stand in a capsule on the Singapore Flyer observatory wheel on 10 September 2015 and 16 July 2015          (Edgar Su/Reuters)
Indonesia fire Singapore smoke haze
Indonesia fire Singapore smoke haze
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The Singapore F1 Grand Prix night race Marina Bay street circuit is seen on 14 September 2015 and 17 September 2013          (Edgar Su/Reuters)
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The Flower Dome and Cloud Forest conservatories of Gardens by the Bay in Singapore on a hazy day on 10 September 2015 and on a clear day on 16 July 2015          (Edgar Su/Reuters)

The smog is caused by firms and smallholder farmers clearing land for palm or pulp and paper. Major plantation companies like Asia Pulp and Paper say they have a "zero burning" policy but have often been criticised by green groups for not doing enough to stop the haze.

A state of emergency has been declared in Indonesia's Riau and Central Kalimantan provinces. More than 135,000 Indonesians are reported to be suffering from respiratory diseases. Schools in Riau province are shut. Students are expected to return to school on 30 September, but if the situation worsens, schools could remain closed.

Indonesia has faced criticism for turning down offers of help from Singapore. Indonesian officials, including vice president Jusuf Kalla, have repeatedly said they have enough resources to handle the crisis. Kalla said that neighbouring countries "enjoy 11 months of clean fresh air from Indonesia" and suggested that it is not a big deal if they suffer from the haze for one month.