People wearing masks walk at the haze-shrouded shopping district of Orchard Road in Singapore on Thursday.

Reuters, AFP/Singapore

Singapore will close all primary and secondary schools on Friday as worsening pollution causes air quality to deteriorate, the Ministry of Education said late on Thursday.

Slash-and-burn agriculture in neighbouring Indonesia has blanketed Singapore in a choking haze for weeks, and the air quality has worsened since Wednesday night.

The three-hour Pollutant Standards Index (PSI) reading climbed to 314 and the 24-hour figure rose to 223-275 at 10 pm local time. Anything over 300 indicates "hazardous" air quality and 201-300 is "very unhealthy", Singapore's National Environment Agency says on its website.

Kindergartens run by the Ministry of Education and special education schools will also be closed, according to a statement on the ministry's website.

In addition, Singapore Sports Hub, which includes an outdoor stadium and an aquatic sports centre, said on its website that it would suspend all outdoor activities. Fast-food restaurants, including KFC, Pizza Hut and McDonald's, have halted delivery service as the pollution worsens.  

Thick grey smoke blown in by southerly winds smothered the island, shrouding the skyline and creeping into homes, with many residents avoiding going outdoors.

"The hazy conditions in Singapore have further deteriorated since last night, as denser haze from Sumatra has been blown in by the prevailing southerly winds," the National Environment Agency said in an advisory.

‘Avoid outdoors’

The agency advised healthy persons to "avoid prolonged or strenuous outdoor physical exertion" and urged the elderly, pregnant women and children to minimise outdoor exposure.

Housewife Asnah Mohamad, 62, said she and her friend used their headscarfs to cover their face as they travelled to a mosque to celebrate Eid al-Adha.

"My husband cannot leave the house because he has a heart condition so I represented him to collect the meat offerings," she told AFP.

"We hope it gets better soon. But what can you do? Go over there (to Indonesia) and pour water on the fire?"

Businesses complained of a low turnout of patrons especially during a holiday, local media reported.

Minister for Social and Family Development Tan Chuan-Jin in a Facebook post late on Thursday called for calm.

"At all times refer only to official channels for information and do not circulate speculations," he wrote.

The city-state, which prides itself for its clean environment, has been cloaked in the haze in varying degrees for about three weeks, the worst such episode since mid-2013.

But Southeast Asia's most damaging cross-border bout with haze was in 1997-1998 when the smog caused an estimated $9bn in losses in economic activity across the region.