JAKARTA, Indonesia — Four people died and two others suffered severe burns while battling a wildfire in a national park on Indonesia’s main island of Java, after they became trapped by thick smoke and rapidly spreading flames, officials said Friday.

The blaze erupted in recent days in the Mentigen and Pusung Lingker areas of the popular Bromo Tengger Semeru National Park in East Java’s Probolinggo regency.

The victims were among a 12-member firefighting team consisting of national park personnel, members of a community fire brigade and local volunteers trying to contain the wildfire on Thursday, said East Java police spokesperson Jules Abraham Abast.

Strong winds fanned the flames and caused the fire to spread quickly through dry vegetation. At about 1:30 p.m., firefighters operating outside the danger zone received an emergency call from colleagues who had become trapped by dense smoke and advancing flames, Abast said.

The fire follows a major blaze in August that scorched nearly 9 square kilometers (3.5 square miles) of grassland and vegetation, including protected edelweiss flowers, in the park.

Rescuers later found three people dead and three others suffering severe burns at an evacuation point. One of those suffering burns died while receiving treatment, Abast said.

Two volunteers remained hospitalized with serious burn injuries after being transferred to Dr. Soetomo General Hospital in Surabaya for specialized treatment. Six others escaped unharmed.

“The incident occurred in a remote mountainous area, complicating rescue efforts,” said Probolinggo police chief Asmida Rizki Siregar, who joined emergency crews carrying victims on stretchers for about 2 kilometers (1.2 miles) because steep terrain prevented vehicles from reaching the site.

She said authorities completed the evacuation late Thursday and have launched an investigation into the deaths, including whether negligence or criminal wrongdoing contributed to the tragedy. Investigators were collecting evidence and interviewing survivors.

The deaths came as Indonesia intensified efforts to combat forest and land fires that have worsened this year as El Niño intensifies a prolonged dry season. Contributing factors also include land clearance using fire in the Indonesian part of Borneo and regions of Sumatra Island, as well as water shortages that have hampered Indonesian firefighters, who have received assistance from Japan.

Indonesia’s Forestry Ministry recorded 799 hotspots nationwide as of Thursday evening, up sharply from 372 a day earlier. More than three-quarters were concentrated in six fire-prone provinces on Sumatra and Borneo.

Toxic haze and smoke have caused a health crisis in neighboring countries as well. The smoke has drifted as far as the Philippines, more than 800 kilometers (500 miles) away.

The surge in fires has renewed concerns about transboundary haze across Southeast Asia. Malaysia on Friday ordered hundreds of schools closed in several states because of deteriorating air quality.

Malaysian Foreign Minister Mohamad Hasan rejected calls from some lawmakers to seek compensation from Indonesia, saying the crisis should be addressed through diplomatic engagement and ASEAN mechanisms. He said Malaysia was coordinating assistance for Indonesia and would push for stronger regional cooperation on haze management.

Singapore also called for closer cooperation. Prime Minister Lawrence Wong said authorities were investigating companies allegedly linked to Indonesian forest and peatland fires that have worsened the haze and would pursue action under Singapore’s Transboundary Haze Pollution Act where warranted.

Indonesia’s Forestry Ministry recorded more than 2,020 square kilometers (780 square miles) of burned land between January and July, almost three times Singapore’s size. The independent Nusantara Atlas project, which monitors fires using satellite imagery, estimated that nearly 8,960 square kilometers (3,460 square miles) of land had burned by the end of August in Indonesia.

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Associated Press writers Edna Tarigan in Jakarta, Indonesia, and Eileen Ng in Kuala Lumpur, Malaysia, contributed to this report.