SINGAPORE - The eastern part of Singapore has been seeing hazier skies with the Pollutant Standards Index (PSI) hitting the moderate range since morning. At 2pm, the three-hour PSI reading was 79. The rest of the country saw PSI readings between 56 and 63 at 2pm.

Residents in the east had complained of a strong burning smell on Thursday evening, with some saying that it smelled like burning plastic.

Residents in areas like Siglap, Bedok, Pasir Ris and East Coast Road said they were affected as early as 6.30pm.

As of 9.30pm, the Singapore Civil Defence Force confirmed that there had been no fires reported in the affected areas.

The National Environment Agency (NEA) said in a statement on Friday that it was alerted to the burning smell experienced by residents in Pasir Ris, Tampines and Bedok on Thursday night. It added that it had contacted its Malaysian counterparts to ask if there had been changes in the air quality in Johor.

A check on the NEA's app MyEnv showed that the hourly PM2.5 reading in the east peaked at 155 at 3am on Friday, an extremely high reading compared to the other parts of Singapore.

It dropped to 24 at 4am and at 8am, it registered a reading of 51. At 2pm, it was 22.

The PM2.5 reading for the rest of Singapore hovered in the 20-26 range at 2pm.

PM2.5 are small, toxic particles that can be emitted by forest fires, vehicles, power plants, refineries, ships and aircraft, and to a lesser extent by construction and land reclamation.