JAKARTA, Indonesia (AP) -- Indonesian authorities closed an airport on Indonesia's Sumatra island Friday due to poor visibility caused by smoke from raging fires burning through peatland, while schools in several provinces closed due to the hazardous haze.
Fluctuating visibility that at times was just 300 meters (yards) forced airlines to postpone flights to the main airport in Pekanbaru, the capital of Riau province, said Yogi Prasetyo, the airport's executive general manager. Poor visibility had also caused delays at an airport in Dumai, another city in Riau.
Worsening haze meant more school Riau and Jambi provinces were closing, education office officials there said. Health offices in both provinces showed more than 300,000 people suffered respiratory illnesses since the haze began and officials said more people have been seeking medical help for respiratory ailments in recent weeks.
Nearly every year, Indonesian forest fires spread health-damaging haze across the country and into neighboring Malaysia and Singapore. The fires are often started by smallholders and plantation owners to clear land for planting.
Many areas of Indonesia are prone to rapid burning because of the draining of swampy peatland forests for pulp wood and palm oil plantations.
Indonesia's Disaster Mitigation Agency late Thursday said there were more than 3,600 hotspots on Sumatra and Borneo islands, leading to very poor air quality in six provinces with a combined population of more than 23 million.
It said 37 helicopters have dropped nearly 240 million liters (63 million gallons) of water and more than 160,000 kilograms (350,000 pounds) of salt for cloud seeding as part of the firefighting efforts.
Indonesian authorities have deployed more than 9,000 people to fight the fires, which have razed more than 328,700 hectares (812,000 acres) of land across the nation, with more than half in the provinces of Riau, Jambi, South Sumatra, West Kalimantan, Central Kalimantan and South Kalimantan.
Record Indonesian forest fires in 2015 spread haze across a swath of Southeast Asia, and according to a study by Harvard and Columbia universities, hastened 100,000 deaths.