KUALA LUMPUR, Malaysia — Hazardous, thick smog triggered by forest fires in Indonesia blanketed parts of Sumatra on Monday and reduced visibility elsewhere in Malaysia.
The pall, caused by deliberately set fires to clear land for plantations, raised fears of a return to the health crisis of 1997 when forest-fire smoke covered several parts of Southeast Asia, triggering tourist cancellations by the thousands.
Environmentalists and opposition groups criticized regional governments for not having learned their lesson and for not revealing more detailed information about the health risks.
They also raised fears about the economic cost to the region, still recovering from the 1997-1998 financial crisis.
Air-pollution levels in the worst-hit areas of Indonesia's Sumatra have risen to around 400 points on the Air Pollution Standard index, well above the hazardous level of 300 points.
Healthy air normally has a reading below 50 points.
"Thick smog blankets the city in the mornings but usually clears after 9 a.m.," said Ardhi Yusuf, an official at the Sumatra Environmental Supervising Body.
Many of the fires are centered deep in the north of Riau province, which is not far from Malaysia and Singapore.
The main hot spots in Sumatra are quite far from key cities in Riau, resulting in little impact on the palm oil and crude-oil industries. The 1997 fires caused thick smog over Malaysia and Singapore, and reached as far north as Thailand and the Philippines.
But favorable winds have kept smoke away from Singapore this time around. Thailand is also smog-free.
Malaysia airport officials said so far there had not been any cancellations of incoming or outbound flights.