Organisers of the Singapore Grand Prix say the haze situation caused by forest fires in Indonesia is volatile but there are no plans so far to cancel the event.

Rain gave the city a welcome respite from the acrid smog but the Pollutant Standards Index (PSI) which measures air quality remained at “unhealthy” levels and grey, fog-like smoke still shrouded the island.

Organisers said on Tuesday there were no plans to amend the program of the nightime street circuit race and the glitzy public entertainment shows that come with it based on the current air quality levels.

“The haze situation is highly changeable – not only from day to day, but from hour to hour,” Singapore GP said in a statement.

“Therefore, it is currently not possible to reliably predict what the PSI level might be over the race weekend.”

Indonesia on Tuesday deployed an extra 1600 military personnel to fight seasonal forest and farm fires on Sumatra island across the Strait of Malacca from Singapore.

Air pollution indices in Singapore were still in the moderately unhealthy range on Tuesday but businesses and schools were operating normally.

They reached very unhealthy levels after sunset on Monday, limiting visibility in the Marina Bay district where the race would be staged with parties and outdoor concerts on the sidelines.

In Malaysia, the education ministry ordered schools closed in Kuala Lumpur, three adjacent states and the administrative capital of Putrajaya.

Singapore GP said the air quality readings and relevant health advisory would be posted on its website and official mobile app to help fans “make informed decisions”.

They will also be flashed on the giant screen in between races and broadcast on the in-circuit radio system. The health advisory will be posted on all entrances at the circuit.

It said protective respiratory masks “will be available for patrons throughout the circuit park at cost price”, while medical and first aid posts would be on standby “to handle any possible haze-related conditions”.

International acts Bon Jovi, Maroon 5, Pharrell Williams, Spandau Ballet and Jimmy Cliff are the featured off-track performances this year.