Brazil's Amazon rainforest has witnessed tens of thousands of fires so far this year, with some of the most intense blazes to ravage the region for almost a decade.

According to the Brazilian space agency, the National Institute for Space Research, there have been more than 75,000 forest fires in the country since January – an 84 per cent increase on the same period in 2018.

More than 9,000 fires have been recorded in the last week alone.

But why is Brazil's rainforest on fire – and is it as bad as images suggest?

What is causing the fires?

It is common for the Amazon to witness fires during the dry season – which runs from July to October – but satellite images show the burning this year is spreading at an unprecedented rate.

On Wednesday, the smoke from the fires was so bad that it caused an hour-long blackout in Sao Paulo, located almost 1,700 miles away. The clouds can also be seen from space.

The Amazon is the world's largest rainforest and is home to about three million species of plants and animals, and some one million indigenous people.