Singapore has closed its schools after the pollution levels caused by the smoky smog enveloping the city hit dangerously high levels.

On Thursday night local time the Ministry of Education said it would close primary and secondary schools on Friday, along with government-run kindergartens, after the Pollutant Standards Index (PSI) reading, which measures how polluted the air is, hit 314 and the 24-hour figure rose to 223-275 at 10pm local time on Thursday. Anything over 300 indicates "hazardous" air quality and 201-300 is "very unhealthy", Singapore's National Environment Agency said on its website.