KUALA LUMPUR, June 20 — Dangerous air quality in Muar led some kindergartens to send their wards home today, as the haze from neighbouring Indonesia continues to return with a vengeance.

According to the Meteorological Department, the air pollutant index (API) in Muar is now at 337. Kota Tinggi also peaked at 211, while Pasir Gudang and Larkin Lama hit 190 and 171 respectively.

By official measures, API readings between 51 and 100 are considered “moderate”, while the 101 to 200 range is considered “unhealthy”. Air quality between 201 and 300 is “very unhealthy” while “hazardous” is applied to API scores topping 300.

Schools in the state hitherto remain open in the absence of a directive from the Johor Education Department, which led some parents to grumble over the silence from officials despite the blanket of smog.

The haze is expected to persist throughout today because of the wind direction.

In Singapore, the Health Ministry has advised residents to limit prolonged or heavy outdoor activities.

Indonesia’s Meteorological Department also reported a surge in the number of hotspots in Riau and surrounding provinces, which shot up to 187 on Tuesday from 113 the day before.

Southeast Asia’s worst haze crisis took place in 1997-1998, causing widespread health problems and costing the regional economy billions of dollars as a result of business and air transport disruptions.

The now-annual affair triggered allegedly due to land-clearing activities by plantation firms in Indonesia has also caused friction among the Asean neighbours, with regular bouts of finger-pointing over which was ultimately to blame for plunging the region into smog.