HONG KONG (CNN) -- Singapore's pollution standards index (PSI) tipped the scales at 401 at noon on Friday, the highest ever recorded, as the government warned that the lingering haze could last for weeks.
The National Environment Agency warned the elderly, pregnant women, children and those with heart and lung conditions to remain indoors as the index hit an historic high. An index reading above 300 is defined as "hazardous" and is regarded as potentially life threatening to the ill and elderly.
Meanwhile, Singapore's Prime Minister Lee Hsieng Loong warned residents angry about the smoke wafting in from Indonesia that they may have to learn to live with it, for now.
"We can't tell how this problem is going to develop because it depends on the burning, it depends on the weather, it depends on the wind," he told a press conference on Thursday.
"It can easily last for several weeks and quite possibly it could last longer until the dry season ends in Sumatra which may be September or October."
The Straits Times reported that queues had formed outside pharmacies across the island on Friday morning and that many had sold out of the particulate-filtering N95 respiratory masks within minutes.
While schools remained closed in Singapore for the summer break, more than 300 were shut temporarily in nearby Malaysia due to the haze. Many office workers in the city-state, meanwhile, struggled to get to work through the haze-shrouded central business district.
"It looks like footage of London smog in the 1950s, except that it smells like a day-old hearth," a British expat energy sector analyst, who did not want to be named, told CNN.
Singapore's Minister for the Environment, Vivian Balakrishnan, flew to Jakarta on Thursday evening to meet with his Indonesian counterparts in a bid to coordinate a response to the smoke problem. The haze, caused by seasonal burn off in Sumatra, has strained relations between the two countries which normally share friendly ties.
"Singapore should not be behaving like a child and making all this noise," senior Indonesian minister Agung Laksono told a press conference on Thursday. "It's not what Indonesians want, it's nature."
Singapore -- which prides itself on its good air quality and green credentials - -- has blamed Indonesian commercial interests for causing the smoke problem.
"Singaporeans have lost patience, and are understandably angry, distressed and concerned," Balakrishnan said on his Facebook page. "No country or corporation has the right to pollute the air at the expense of Singaporeans' health and wellbeing."
Jakarta, meanwhile, has pointed the finger at Singaporean palm oil ventures which it says have caused the smog by clearing land to make way for plantations that provide the feedstock for city-state's refining industry.
"The slash-and-burn technique being used is the cheapest land-clearing method and it is not only used by local farmers, but also employees of palm oil investors including Singaporean and Malaysian companies,'' Hadi Daryanto, a senior official at Indonesia's Forestry Ministry, told Indonesian media.
"We hope the governments of Malaysia and Singapore will tell their investors to adopt proper measures so we can solve this problem together.''
Three Singapore-based palm oil companies with land concessions in Indonesia, including Wilmar International Ltd, Golden Agri-Resources Ltd and First Resources Ltd, said this week they had "zero burning" policies and used only mechanical means to clear land.
Singapore's Prime Minister Lee said the city-state had provided satellite data to Indonesia to help identify who was responsible for the fires.
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