The haze in Singapore been worsening again since early Tuesday morning, with the three-hour Pollutant Standards Index (PSI) rising to 123 at 11am.

The first PSI reading of the day at 6am was 109, but by 9am it had risen to 115 and has been climbing since.

Any reading above 100 means unhealthy air quality.

The haze, caused by forest fires in Sumatra, Indonesia, was particularly bad at 10pm on Monday night when the PSI hit 155.

The National Environment Agency has said that the hazy conditions are expected to persist for the next few days. It has advised that children, the elderly and those with heart or lung diseases reduce prolonged or heavy outdoor activities. Everyone else should limit prolonged or heavy outdoor activities.