The number of hotspots increased significantly from only three on Saturday, Slamet Riyadi, spokesman of the Pakanbaru meteorology station, said.
Of the 37 hotspots, 25 were found in Bangka Belitung, six in South Sumatra, three in Lampung, two in Bengkulu, and one in Riau.
In Riau, the one hostpot was detected in Kampar District and it was not developed into a fire, he remarked.
The government has claimed that the number of forest fire cases had drastically dropped by 78 percent until August this year, compared to last year.
President Joko Widodo (Jokowi) had earlier instructed that action must not be delayed to put an end to fires when they were still easier to control.
The order was given to prevent a recurrence of the 2015 land and forest fires that had produced smoke chocking hundreds of thousands of Sumatran and Kalimatan inhabitants, and spreading up to Malaysia and Singapore.
The legal enforcement has also been stepped up to prevent fires intentionally set in farmland and plantation areas particularly.(*)