The fire, which began last week, affected almost 900 hectares across the Bromo Tengger Semeru National Park as of Tuesday, burning large areas of dry grassland, vegetation and protected edelweiss flowers, said Rudijanta Tjahja Nugraha, head of the park located in East Java province.
The volcanic landscape of Mount Bromo, one of Indonesia's best-known attractions, is in the affected area and has been closed as firefighters work to prevent the blaze spreading in the conservation zone.
Active hot spots remain in four areas within the park: Watangan, Argowulan, Dingklik-Pakis and Bincil-Mungal.
Teams had been working to prevent flare-ups on the ground and with aerial operations, Nugraha said.
"We are not only trying to put out the fire, but also ensuring it is completely extinguished and does not re-emerge," Nugraha said.
The Bromo fire comes as Indonesia faces a growing wildfire crisis during the dry season.
The National Disaster Management Agency, or BNPB, said nearly 48,900 hectares of peatland had burned across six fire-prone provinces as of Monday, with the largest affected area in West Kalimantan on Borneo island.
In the provincial capital Pontianak, schools suspended in-person classes after air quality deteriorated to unhealthy levels and health officials reported a rise in respiratory illnesses.
The government has intensified firefighting efforts across Sumatra and Borneo islands, deploying more than 35 aircraft including water-bombing helicopters and patrol planes.
"Aerial operations are supporting ground operations which are especially critical in peatland areas," said BNPB chief Suharyanto, who like many Indonesians uses a single name.
"Because peat fires can continue smouldering underground long after surface flames disappear and can reignite if not fully extinguished."
Peatland fires generate dense smoke that contributes to hazardous haze, worsening air quality and increasing health risks across affected areas, sometimes even in neighbouring countries, he said.
Satellite imagery shows a haze of wildfire smoke drifting from West Kalimantan into neighbouring Malaysia on several days this month, according to BNPB.
Forest and peat fires are an annual problem in Indonesia, which strains relations with neighbouring countries.
Fires are often started illegally by plantation owners or traditional farmers to clear land for planting and those burns periodically blanket parts of Southeast Asia in hazardous haze.
