Toxic haze from Indonesian forest fires closed thousands of schools across the country and in neighbouring Malaysia on Wednesday, while air quality worsened in Singapore just days before the city’s Formula One motor race.

Forest fires are blazing on the islands of Sumatra and Borneo, with Jakarta deploying thousands of security forces and water-bombing aircraft to tackle them.

The Indonesian blazes are an annual problem, but this year’s are the worst since 2015 and have added to concerns about wildfire outbreaks worldwide exacerbating global warming.

The smog is also affecting endangered orangutans on Borneo, with dozens of the young apes at rescue centres contracting respiratory infections, according to the Borneo Orangutan Survival Foundation.

Borneo island is divided between Indonesia, Malaysia and Brunei.