Air pollution levels in Singapore reached unhealthy levels ahead of this weekend's grand prix, as authorities continued to monitor the situation.
A state of emergency was declared in Indonesia as forest fires continued to worsen the air quality in the Riau province in Sumatra.
That has expanded to neighbouring countries Singapore and Malaysia.
The 24-hour Pollutant Standards Index (PSI) at 5pm local time was between 119 and 147, Singapore media reported on Monday.
The unhealthy range is 101-200.
On Monday, helicopters water-bombed forest fires in Indonesia, using chemicals produced to induce rain in the area.
The haze was so thick last week, that aircraft were unable to fly.
Singapore Grand Prix organisers said they were monitoring the situation closely and working with the relevant agencies "before making any collective decisions regarding the event".
"The possibility of haze is just one of the many potential issues that are covered in the contingency plan," a Singapore GP spokesperson said.
Watch our preview of the Singapore event in this week's Inside Grand Prix show.