SINGAPORE (AP) — Singapore urged people to remain indoors amid unprecedented levels of air pollution Thursday as a smoky haze wrought by forest fires in neighboring Indonesia worsened dramatically. Nearby Malaysia closed 200 schools and banned open burning in some areas.

The Pollutant Standards Index, Singapore’s main measure for air pollution, surged to a record reading of 371, breaching the “hazardous” classification that can aggravate respiratory ailments. The previous all-time high before this week was in 1997, when the index reached 226.

(READ MORE: Singapore’s PSI hits 371 as government demands action)

The hazardous reading lasted three hours before easing to 253 in the evening, still “very unhealthy.”

Smog fueled by raging Indonesian blazes has hit Singapore and Malaysia many times, often in the middle of the year, but the severity of this week’s conditions has strained diplomatic ties. Officials in Singapore say Jakarta must do more to halt fires on Sumatra island started by plantation owners and farmers to clear land cheaply.

“This is now the worst haze that Singapore has ever faced,” Singapore’s Environment Minister Vivian Balakrishnan wrote on his Facebook page. “No country or corporation has the right to pollute the air at the expense of Singaporeans’ health and wellbeing.”

The haze has shrouded the city-state’s skyscrapers in a pall of noxious fumes and posed numerous inconveniences for Singaporeans, some of whom complained of coughs and covered their faces with handkerchiefs while walking outdoors.

A smoggy sunrise in Singapore. Haze triggered by forest fires in neighboring Indonesia has caused air pollution to briefly hit its worst level in nearly 16 years in June. Pic: AP.

Flight controllers at Singapore’s Changi Airport were instructed to take precautions because of lower visibility, while McDonald’s said it was temporarily halting delivery service to protect its workers’ health.

Some hospitals shut windows in wards with elderly patients to keep out the acrid odor of burning. Sports organizers canceled several football and sailing competitions this weekend.

Prime Minister Lee Hsien Loong advised residents to stay indoors as far as possible, adding that “we will get through this together.”

Lee told a news conference Thursday that the haze was expected to persist for an unknown number of days because of wind and weather conditions. He announced that a government panel was being formed to protect public health and the city-state’s economic resilience.

In neighboring Malaysia, air quality remained relatively unaffected in the country’s biggest city, Kuala Lumpur, but a southern state that borders Singapore also recorded “hazardous” pollution in one district, where 200 schools were ordered shut through at least Friday. The Department of Environment banned open burning and made it punishable by up to five years in prison in three states separated from Sumatra by the Malacca Strait.

Indonesian officials have defended their response to the haze, saying the government is educating farmers about alternatives to traditional slash-and-burn agriculture. Some Indonesian officials have also suggested that some fires might be blamed on Singaporean and Malaysian companies involved in Indonesia’s plantation industry.