Singapore’s pollution levels set a new record for a third day in a row on Friday, as smoke continued to drift in from Indonesia’s Sumatra Island, where plantation workers and farmers have started a fire to clear land cheaply.

People on the streets covered their faces with masks and handkerchiefs, while flight controllers at Singapore’s Changi Airport were instructed to exercise precaution because of reduced visibility, as the Pollutant Standards Index hit 401, the highest in the country's history, on Friday noon (12:00 a.m. EDT). Hospitals shut windows and ventilators, while sports events and meets scheduled for the weekend have been cancelled.

Neighboring Malaysia is also being affected by the Sumatran fires, and has closed dozens of schools and banned open burning in some areas. In the past, Singapore and Malaysia have dealt with smog, fuelled by Indonesian fires, but the severity of this week’s pollution has led to diplomatic tensions.

“On the international front, we need urgent and definitive action by Indonesia to tackle the problem at source. Singaporeans have lost patience, and are understandably angry, distressed and concerned,” Singapore’s Environment Minister Vivian Balakrishnan wrote on his Facebook page. “This is now the worst haze that Singapore has ever faced.”

He asked Singaporeans to limit prolonged outdoor activities, while children, elderly and those with heart or lung conditions were asked to avoid going outdoors altogether.

“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,” Singapore's Prime Minister Lee Hsieng Loong told a press conference on Thursday, CNN reported. “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.”

Indonesia’s Coordinating Minister for People’s Welfare, Agung Laksono, dismissed Singapore’s complaints, saying: “Singapore should not act like children, making all that noise,” the Globe and Mail reported.

The Indonesian government, according to authorities quoted in the Globe and Mail, are working toward persuading farmers to use environment-friendly alternatives to traditional slash-and-burn agriculture.

Malaysia’s air quality remains relatively unaffected, but a region in the country's south bordering Singapore recorded “hazardous” pollution, prompting authorities to shut down several schools, the CNN report said.