BSS/AFP) - Four men have died fighting wildfires in a national park on Indonesia`s Java island, the forestry ministry said Friday, as the southeast Asian country battles a months-long crisis of blazes and toxic smoke.

The four were overwhelmed while battling flames Thursday in the Bromo Tengger Semeru National Park in East Java, a ministry statement said, without providing details on who the individuals were.

Two others suffered serious burns.

Two of the fallen men were national park officers and two were security guards helping them, according to national park spokesman Endrip Wahyutama.

They had been trapped by flames and thick smoke. Three died at the scene and a fourth fourth later in hospital.

A volunteer firefighter and a security guard from a nearby hotel who also jumped in to help were receiving medical treatment, said Endrip.

A volunteer firefighter and a security guard from a nearby hotel who also jumped in to help were receiving medical treatment.

"This incident serves as a reminder that forest and land fire extinguishing is a high-risk operation," said the ministry.

It said there had been a jump in hotspots detected by satellites as areas of unusually high temperatures but do not necessarily translate into individual fires.

By Thursday evening, the number of hotspots stood at 799 nationally, up from 372 a day earlier.

Most were in Central Kalimantan, a province on Borneo island that Indonesia shares with Malaysia and Brunei, followed by the south of Sumatra island.

"Central Kalimantan recorded the largest increase (in hotspots), so field operations are being strengthened," said the statement.

The ministry expressed particular concern about an area around the Tanjung Puting National Park, an important habitat for endangered orangutans.

Water-bombing and cloud-seeding operations to make rain have been hampered by low visibility due to smoke from the fires, it added.

The ministry said several locations in Sumatra and Kalimantan were experiencing "unhealthy to very unhealthy conditions, even locally hazardous" due to the haze emitted by the blazes, turning the sky in some areas orange.

"If air conditions worsen, people are advised to reduce outdoor activities and wear masks when outside," it said.