Indonesia is to use weather changing technology to try to produce rain to put out raging fires on Sumatra island that have cloaked neighbouring Singapore in thick haze.

The city-state, home to 5.3 million inhabitants, has been pressing Jakarta to take action over the fires which have pushed air pollutant levels on the island to a 16-year high.

The government planned to use a technology called “cloud-seeding” to try  put out the fires, that are mainly centred on peatlands in Riau province, said Indonesian forestry ministry official Raffles Panjaitan.

Helicopters would be sent into the skies above Sumatra to inject chemicals into clouds, which prompt the formation of heavy ice crystals, and so speed up the production of rain, he said.

But the helicopters, from the disaster management agency, will not be dispatched until Friday at the earliest, he added.

About 100 firefighters are tackling the blazes but finding them hard to extinguish because they are smouldering underground in carbon-rich peatland, mostly in palm oil plantations.

“It is extremely difficult to extinguish the fires which are burning under the surface of the peatland,” Mr Panjaitan said.

He said the cloud-seeding operation would depend on weather conditions. “Hopefully there will be lots of clouds so that we can produce a lot of rain.”

The worst affected area is Bengkalis district, where 650 hectares (1,600 acres) of land is ablaze – 555 fires have been detected in Riau so far, up from 356 last month.

In Singapore, the Pollutant Standards Index soared to 172 at 3pm local time (0700 GMT), well past the officially designated “unhealthy” threshold of 100, according to the National Environment Agency website.

It was Singapore’s worst haze reading since September 1997 when the number peaked at 226.

The haze problem is a recurring one which happens in the dry season as a result of forest fires in the sprawling Indonesian archipelago, some of them deliberately started to clear land for cultivation.

Read more: Sky News