A view of the Marina Bay Sands casino and hotel and the skyline of Singapore's central business district Reuters

Singapore air quality has improved as the 24-hour Pollutant Standards Index (PSI) returned to the moderate range at 70-100 on Sunday, after the nation experienced haze conditions for two days.

The three-hour PSI was recorded at 70 while the one-hour PM2.5 was in the normal range in all regions across the country.

The National Environment Agency (NEA) said that this improvement has been possible as less dense haze was blown from Indonesia's Sumatra into Singapore by prevailing winds.

The agency also added that it is expecting the situation to improve further because of the winds.

On Friday morning, Singaporeans experienced a burning smell as haze from central Sumatra was blown in. The 24-hour PSI increased up to an unhealthy range.

"Given the air quality forecast for the next 24 hours, everyone can continue with normal activities. Persons who are not feeling well, especially the elderly and children, and those with chronic heart or lung conditions, should seek medical attention," NEA told Channel NewsAsia.

The index incorporates six types of pollutants such as sulphur dioxide, particulate matter that is 2.5 micrometres in diameter or smaller (PM2.5), particulate matter that is 10 micrometres in diameter or smaller (PM10), ozone, nitrogen dioxide and carbon monoxide.

Among all these six pollutants, PM2.5 is considered to be highly hazardous. The small size of the particles of PM2.5 enters the human lungs more easily than the others.