Toxic haze from Indonesian forest fires Wednesday worsened air quality to unhealthy levels in neighboring Singapore just days before the city's Formula One (F1) motor race.

The worsening pollution increased fears that this weekend's F1 race may be affected. Organizers say the possibility of haze is one of the issues in their contingency plan for Sunday's showpiece night race, but have not given further details. The city-state's tourism board said spectators would be able to buy masks as protection from the haze if conditions did not improve. Assistance would also be provided on-site for spectators who feel unwell, the board's executive director of sports, Jean Ng, told the Today news portal.

"Various Singapore government agencies have been working closely with the race organizer... to ensure the delivery of the best race and entertainment experience possible while keeping a watchful eye on the health and well-being of everyone involved," she said. Illegal fires to clear land for agriculture are blazing out of control on Sumatra and Borneo islands, with Jakarta deploying thousands of security forces and water-bombing aircraft to tackle them. The Indonesian blazes are an annual problem, but this year is the worst since 2015 and has added to concerns about wildfire outbreaks worldwide exacerbating global warming.