Indonesia on Thursday accused Singapore of acting "like a child" over choking smog from forest fires in Sumatra that has triggered an environmental crisis, as the city-state's premier warned it could last weeks.
The escalation in tensions between tiny Singapore and its vast neighbour came as the levels of haze enveloping the island hit a new record high, shrouding the whole city, from residential blocks to tree-lined parks.
As the acrid smell of burnt wood crept into people's flats and medical masks sold out at drug stores, the city-state's environment chief demanded "decisive action" to address the crisis after talks with Indonesian officials in Jakarta.
Singapore has been ratcheting up pressure for Jakarta to act over one of its worst ever environmental crises -- but Indonesia, which insists companies in the city-state that own plantations on Sumatra also share the blame, hit back.
"Singapore should not be behaving like a child and making all this noise," Agung Laksono, the minister coordinating Indonesia's response, told reporters. "This is not what the Indonesian nation wants, it is because of nature."
Singapore's air pollution index hit a new all-time high Thursday, soaring to 371 at 1:00 pm (0500 GMT), well past the previous record of 321 set the night before, before falling later in the afternoon.
Any reading above 300 is "hazardous" while a reading above 400 is deemed "life-threatening to ill and elderly people," according to government guidelines.
Singapore's prime minister declined to respond to Laksono's provocative comments, saying he did not want to engage in "megaphone diplomacy".
Lee urged people to stay indoors and protect themselves from the haze which has hung over the island since Monday, asking citizens to "look out for one another".
"We cannot tell how the haze problem will develop," Lee told a press conference.
"It can easily last for several weeks and quite possibly longer until the dry season ends in Sumatra."
Andrew Tan, the head of Singapore's national environment agency, said that officials from the city-state and their Indonesian counterparts had a "very frank exchange of views" during the emergency talks in Jakarta.
"The situation is deteriorating," he said. "We have highlighted to our Indonesian counterparts that it is time now for decisive action."
Drug stores in Singapore's central business district were sold out of disposable masks and refused to take advance orders, as the strong odour seeped into homes across the island as well as inside the air-conditioned trains of the metro system.
Parks were empty of the usual morning joggers, but thousands of employees still trooped to offices and labourers continued their work on high-rise buildings under construction.
The previous Singapore air pollutant index high of 226 was recorded in September 1997 at the height of a Southeast Asian calamity also resulting from vast amounts of haze from Indonesia, where slash-and-burn farming generates heavy smoke during the dry season that begins in June.
Parts of Malaysia close to Singapore have also been severely affected by the smog.
Laksono said that plans to use cloud-seeding to unleash rain over Sumatra and put out the fires were also under way, and it was hoped helicopters could be dispatched on Friday.
Haze was also affecting the Indonesian island of Batam, just south of Singapore, where authorities were handing out free masks.
Visibility was poor and people complained of having sore eyes and not being able to breathe properly.
Smallholders and plantations in Sumatra -- some of them with Singaporean investors -- have been accused of using fire to clear land for cultivation, but big palm oil companies deny involvement in such activities.