Singapore's main measurement of air quality has hovered in the "unhealthy" classification as smoke from roaring blazes on Indonesia's Sumatra island drifted across the sea and cast a gray pall over the city-state's skyscrapers.
The readings on the Pollutant Standards Index were mostly between 104 and 123 on Tuesday, within the "unhealthy" range between 101 and 200. A peak reading of 155 on Monday night was the highest since late 1997, when officials reported a 226 reading.
Smoke haze is a nearly annual problem for Singapore and its northern neighbor Malaysia, often beginning in midyear when farmers in Indonesia seek to clear land cheaply by starting fires. It sometimes causes diplomatic strains as Malaysia and Singapore urge Indonesia to do more to prevent illegal burning.
Malaysia has been only lightly affected so far this year, with pollution readings in Kuala Lumpur, Malaysia's largest city, not breaching the unhealthy mark Tuesday. Indonesia has said part of the current problem is caused by peat blazes that firefighters are struggling to put out during hot, dry weather.
Indonesian Forest Ministry spokesman Sumarto Suharno said the government is continuing to educate farmers about alternatives to traditional slash-and-burn agriculture.
"We have been able to reduce the regional haze problem significantly for years with help from local communities and will continue to undertake all efforts to prevent it from spreading," Suharno said.
In Singapore, defense ministry spokesman Col. Kenneth Liow said the armed forces have "reduced physical and outdoor training accordingly" after the pollution index exceeded 100.
Landscaper Hedrick Kwan blamed the haze after his two young sons started coughing as an acrid smell filled the air.
"We usually leave the windows open but now we can't do that because of all the dust and smoke," he said.
The National Environment Agency has advised Singaporeans, especially the elderly, young children and people with respiratory problems, to avoid prolonged exposure outdoors.
Melissa Cheah, a financial sector worker, said her office has discussed the possibility of advising employees to wear protective face masks.
Singapore's Environment Minister Vivian Balakrishnan said his agency is offering assistance to Indonesia to put out the forest fires.
Hospitals and clinics are bracing for more patients in the week ahead.
"Based on what we have seen over the years, when the haze hits us, it takes about three to four days before we see all these additional patients coming in for medication," said family physician Sarani Ng Omar, who expected a rise in asthma-related cases, nasal problems and eye inflammation.
Associated Press writer Niniek Karmini in Jakarta, Indonesia, contributed to this report.