Billowing smoke from Indonesian forest fires has worsened Singapore's air pollution, raising concern among organisers of this weekend's Formula One night race.
Large parts of neighboring Malaysia were also shrouded in the gray, acrid pall, and an Indonesian province declared an emergency that closed schools and limited working hours on Monday.
The Pollutant Standards Index, Singapore's main measure of air pollution, rose to 222 in the early hours of Monday, the highest level in a year and above the official "very unhealthy" bandwidth of 200, according to the National Environment Agency.
Persistent haze over the weekend caused the cancellation of several outdoor events, while some organisers of a run required participants to walk the route instead.
The organisers of the Singapore Grand Prix were also keeping a close watch on the situation. The F1 race, to be held this weekend, has been in Singapore since 2008 and draws hordes of tourists and racing enthusiasts from the region.
"In the event that the haze caused visibility, public health or operational issues, Singapore GP would work closely with the relevant agencies before making any collective decisions regarding the event," the Singapore GP said in a statement.
However, a decision on whether it will be safe to race will be made by FIA Race Director Charlie Whiting after consulting with drivers and teams.
The race has always been held at this time of year, and while there has been some haze in past years due to the forest fires, it has never prevented the race from going ahead.
Tickets for the race have mostly been sold in advance, though uncomfortable atmospheric conditions could affect the turnout at the Marina Bay Circuit.