SINGAPORE - With the haze expected to get worse in Singapore today, organisers of several races have been forced to consider whether they should go on.

The Singapore Cancer Society decided to cancel Sunday morning's Race Against Cancer just after 9pm on Saturday. The society posted on its website that it was calling off the run "for the safety and health of runners, volunteers, staff and beneficiaries".

Participants for Sunday's Yellow Ribbon Prison Run were told to wait till 5am - an hour before it is set to start - before a decision would be taken. It is organised by the Yellow Ribbon Project, which aims to help former prisoners rejoin society. On its website, POSB also said it would make a decision on its Passion Run for Kids depending on the three-hour PSI reading at 5am.

The National Environment Agency (NEA) said on Saturday that the 24-hour Pollutant Standards Index (PSI) is expected to be at the low end of the 101 to 200 unhealthy range today. This may climb into the mid to high sections if denser haze is blown in by unfavourable winds.

The 24-hour PSI was within the moderate range of 51 to 100 for most of yesterday before creeping into unhealthy levels in the evening. By 11pm, the readings were between 90 and 107. The three-hour PSI reading climbed to 147 at 4pm.

The elderly, pregnant women and children are advised to minimise prolonged or strenuous outdoor activity when the 24-hour PSI exceeds 100. Those suffering from chronic lung or heart disease should also avoid such activities.