SINGAPORE - The sky was noticeably greyer than usual on Friday, with the Pollution Standards Index creeping into the unhealthy range in the afternoon.

The three-hour PSI was 65 at around 8am, and it had gone up steadily through the day, peaking at 106 at 6pm. It dipped back into the moderate range of 99 at 8pm.

In a statement issued to The Straits Times at 8.04pm, the National Environment Agency (NEA) said: "It has been hazy in Singapore today. The PM2.5 levels are elevated in most regions of Singapore.

"The haziness is likely due to an accumulation of increased particulate matter in the atmosphere under light wind conditions throughout today. Burning activities in the northern Asean region, Peninsular Malaysia and Sumatra could have contributed to the increased concentration of particulate matter."

"The current hazy conditions are expected to persist for the rest of today. For tomorrow, the prevailing winds are expected to be light and variable in direction, and hazy conditions can still be expected," it added.

The 24-hour PSI at 8pm was between 74 and 86, with the highest reading of 86 recorded in the east of Singapore.

It was 82 in the west, and between 74 and 76 in other parts of Singapore.

NEA advised that reducing outdoor activities and physical exertion can help limit the ill effects from haze exposure, but the air quality is safe enough for people to continue with normal activities.