Singapore's prime minister has warned that the haze engulfing the city-state could last for weeks, as air pollution soared to record levels.
The pollution standards index peaked at 371 on Thursday, breaking previous records and well above hazardous levels, before falling to about 300.
The haze is the result of forest fires started by farmers clearing land on the Indonesian island of Sumatra.
The issue has sparked accusations between the two neighbours.
Dr Vivian Balakrishnan, Singapore's Environment and Water Resources Minister, wrote on his Facebook wall that he would demand "definitive action" from Jakarta.
"No country or corporation has the right to pollute the air at the expense of Singaporeans' health and wellbeing," he said.
However, Indonesian Minister for People's Welfare Agung Laksono said that Singapore was "behaving like a child".
"This is not what the Indonesian nation wants, it is because of nature," he said.
Environment officials from the two nations have been holding an emergency meeting in Jakarta, to discuss the issue.
Since the haze arrived, Singapore's buildings have been obscured by the polluted air and the smell of burnt wood has permeated the city-state.
A PSI reading above 200 indicates "very unhealthy" air, while a PSI score above 300 is "hazardous". Readings are being posted on the website of the National Environment Agency.
At a press conference, Singaporean Prime Minister Lee Hsien Loong said the haze could "easily last for several weeks and quite possibly longer until the dry season ends in Sumatra".
Mr Lee asked Singaporeans to "stay indoors where possible and avoid heavy outdoor activities".
He also announced that the Singaporean government would hold daily press conferences on the haze situation.
Air traffic controllers in Singapore have been told to work with extra caution given the poor visibility, while McDonald's has temporarily cancelled its delivery service.
The Singaporean military has also reportedly suspended all outdoor training.
The poor air quality has prompted widespread buying of disposable face masks, leading shops to run out of stock.
Parts of Malaysia have also recorded "hazardous" pollution levels, with over 200 schools in the country's south ordered to shut.
Malaysia's Department of Environment has also banned open burning in some states.
Indonesia's forestry ministry said it intended to use cloud seeding to try to induce rain on the affected area of Sumatra.
Indonesian officials have suggested that foreign palm oil investors, including Singaporean companies, may bear some responsibility for the fires.
However, several major Singapore-based palm oil companies have denied any involvement.
Singapore's prime minister said the city-state had provided satellite data to Indonesia to help identify who was responsible for the fires.
He added that if any Singaporean companies, or companies with a presence in Singapore played a part in the fires, they would be held responsible.
In 1997 and 1998, many countries in the region were affected by the South East Asian haze, which was caused by smog from Indonesian fires.
Road and air traffic was disrupted, and the smog is thought to have made around 20 million people ill.
The haze led to an agreement on trans-boundary haze pollution being approved by the Association of Southeast Asian Nations (Asean) in 2002.
However, Indonesia has yet to ratify the agreement.