The center uses a four-tier alert system from 0 to 3, where the highest level is activated in the event of a "high risk of severe transboundary haze in the region."
This risk includes the detection of active and persistent fire hotspots, with smog of moderate to severe density spreading over two or more consecutive days, coinciding with continued dry weather and winds pushing the haze toward neighboring countries of the Association of Southeast Asian Nations (ASEAN).
The alert was issued on Friday, noting that similar warnings were issued twice earlier this year, specifically on August 26 and March 27.
The smog, which has persisted for months, has caused a sharp rise in respiratory problems and led to the closure of schools in Indonesia, Malaysia, Singapore, and Timor-Leste.
Singapore ranked second on Saturday in the live ranking by the "IQAir" platform for the world's most polluted major cities, behind Baghdad, while Kuala Lumpur ranked third. All readings showed "very unhealthy" levels.