Smoke billows during a land fire in Musi Banyuasin near Palembang, South Sumatra province, Indonesia, August 14, 2019 in this photo taken by Antara Foto. Antara Foto/Nathan/ via REUTERS

JAKARTA (Reuters) - Indonesia has sealed parts of palm oil and timber concessions owned by 10 companies on Borneo island after a spate of forest fires, authorities said on Thursday, warning those involved in forest burning would be severely punished.

Indonesia is under pressure to end slash-and-burn clearance of land, often on plant palm and pulp plantations. The practice caused devastating fires in 2015 that spread a choking haze across most of Southeast Asia.

The disaster mitigation agency (BNPB) recorded 1,092 hot spots as of Thursday, the highest since the 2015 fires, and at least six provinces on the islands of Sumatra and Borneo have declared an emergency.

About 200 hectares (494 acres) of land had been sealed in Borneo’s West Kalimantan province, the environment ministry said.

Warning letters were also sent to 58 plantation firms with hot spots indicating fire or a high risk of fire, said Rasio Ridho Sani, the ministry’s director general of law enforcement.

“Corporations which are found to be involved in forest burning must be punished severely,” Sani said in a statement.The fires had mostly broken out in palm and timber concessions, said the ministry, which only identified the companies by their initials.

Authorities have deployed 36 helicopters and 9,072 personnel to monitor the situation and put out fires when detected.

President Joko Widodo has threatened to replace military and police officers fighting forest fires from their posts if they fail to extinguish the flames.

In Sumatra, fire had also broken out in Tesso Nilo, a 81,700-hectare national park in the province of Riau, according to the environment ministry. The park is a habitat for critically endangered tigers and elephants.