AS HAZE blanketed the island on Thursday and air quality deteriorated sharply into the unhealthy range, the Singapore Government urged Indonesia to act.

The Pollutant Standards Index (PSI), measured in three-hourly slots, hit 108 at 6pm on Thursday - breaching the unhealthy threshold of 100 for the first time since 2006.

The worsening situation prompted Environment and Water Resources Minister Yaacob Ibrahim and Foreign Minister George Yeo to register Singapore's concerns with their Indonesian counterparts.

The National Environment Agency (NEA) said Dr Yaacob had contacted his Indonesian counterpart Gusti Muhammad Hatta and expressed his deep concern that the haze would deteriorate if Indonesia did not put in place 'immediate and enhanced measures' to put out the hot spots in Sumatra.

Singapore also repeated its earlier offer to assist in fire-fighting efforts.

Singapore's ambassador in Jakarta was also instructed on Thursday to inform the Indonesian Ministry of Foreign Affairs that Mr Yeo wished to speak to his counterpart Marty Natalegawa.

At 10am on Friday, the PSI measured 94.

PSI crosses 100