Updated

A thickening, smoky haze cast a shadow over festivities in Singapore on Thursday, as Muslims headed to mosques to celebrate the culmination of the annual hajj pilgrimage and Chinese readied for a traditional harvest festival.

The three-hour Pollutant Standards Index (PSI), which measures air pollution in the country, hit the day's high of 262 at noon on a public holiday. It then dropped to 225 in the mid-afternoon. The haze is blowing in from neighboring Indonesia where forests are being burned to clear the land for farming, as is done every year causing the annual problem for the region.

Although there are no official air quality descriptors affiliated with the three-hour index, a reading of these levels on a 24-hour index would mean that air quality is in the "very unhealthy" range, according to the National Environment Agency.

The 24-hour PSI at noon had a range of 173 to 216. Anything above the official "very unhealthy" bandwidth of 200 is particularly taxing on young children, the elderly and those with heart or lung diseases.

High-rise buildings surrounding Masjid Hajjah Fatimah, a mosque in an area historically associated with the island nation's Malay community, were barely visible through the veil of smog.

While some faithful were seen covering their mouths to block out the haze, none wore masks as prayers conducted inside the mosque required them to wash their faces.

Mustafa Muhamad, 61, said the bad air quality caused some of his friends to opt to say prayers to mark the Eid-al-Adha, or festival of sacrifice, at home instead. From a group of 40 usually seen at each of the day's five prayer sessions, the number has dwindled to around 20, he added.

"The haze is very bad, there are less people in the mosque this year. Coming the mosque to pray used to be very nice because we would mingle around after," the teacher explained.

At the nearby Sultan Mosque, tourists were seen decked in masks while taking pictures with its iconic facade.

Preparations for the Chinese mid-autumn festival on Sunday, where farmers traditionally celebrated their harvest, were in full swing.

One such celebration will feature giant lantern sets, nightly cultural performances and a food street.

"My son is very sensitive to dust and has lung issues, so I'm limiting his outdoor time," said Esther Au Yong, 34, a freelance editor. A trip to the gardens with her three-year-old son on Friday night, on an outing organized by his kindergarten is on the rocks due to the haze.

On Tuesday, Indonesia's environment and foresty ministry named four Indonesian plantation companies whose licensed were suspended or revoked for clearing land illegally, sparking forest fires in the process.

Some 27 companies are being investigated in linkage to the forest fires, Indonesian authorities said, while 140 individuals are being questioned. A Singapore-listed firm is among those under investigation.