HAZE from Indonesia brought Singapore's air pollution to its worst level in four years on Wednesday, and the smoke is expected to remain in the air until at least Saturday.

The situation could worsen, as fires continue to burn in parts of Sumatra being cleared by farmers, and prevailing winds blow more smoke this way.

But some relief might come from showers expected this week, the National Environment Agency (NEA) said on Wednesday.

The Pollutant Standards Index (PSI) hovered at 80 on Wednesday, the highest 24-hour recording since 2006 when Singapore was last blanketed by a severe haze. A PSI of 80 puts the air quality in the moderate range. On Wednesday night, the three-hour PSI was 74 between 7pm and 10pm.

The NEA has advised those with pre-existing respiratory and heart conditions to refrain from outdoor activities for now.

Expressing disappointment at the recurrence of the haze problem, Minister for the Environment and Water Resources Yaacob Ibrahim said yesterday that Singapore may register its concerns with the Indonesian authorities 'more strongly' if the situation worsens.

Air quality worst since 2006