Thai authorities used helicopters Thursday to try to contain a fire that overnight engulfed two mountains on largely undeveloped forest land in a province northeast of the capital Bangkok.

The fire broke out Wednesday night in Nakhon Nayok province, 70 miles northeast of Bangkok, but firefighters could not directly tackle it because the mountains are too steep to safely climb, especially in the darkness of night, provincial Governor Bancha Chaowarin told reporters.

"Apart from the wind’s direction, I also have to look after the lives and safety of those conducting the operation. After reviewing the situation, since it is at a mountaintop, we had to retreat to standby and convene over what we can do," Bancha said late Wednesday night.

At least 10 firefighting vehicles were dispatched to battle the blaze, and they were joined Thursday afternoon by at least two helicopters, which surveyed the situation and dumped water.

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Initial efforts to contain the blaze had concentrated on creating firebreaks.

Bancha was quoted by the newspaper Thai Rath as saying it was initially estimated the fire could be brought under control within five days, but that he would try to do it in just three.

Other forest fires have broken out in recent days in provinces farther north as seasonal temperatures rise, a perennial problem that contributes to dangerously high levels of air pollution.

About 275 acres of forest in Nakhon Nayok had been burned by noon Thursday as the fire continued to smolder, Bancha said.

The fire began on a high part of Khao Chaplu mountain and then spread to the adjacent Khao Laem mountain. Local media said it burned easily because much of the growth was bamboo, and high winds fanned the flames.

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The mountains sit in a vast parcel of land not far from one of the country’s best known nature reserves, Khao Yai National Park. Chulachomklao Royal Military Academy, Thailand’s version of West Point, is close to where the fire broke out and a village of about 500 residents is about half a mile from the fire site, Thai Rath reported. Residents were warned to alert officials about any wild animals they saw fleeing the burning forest.

Prime Minister Prayuth Chan-ocha was closely monitoring the situation and had ordered officials and the army to mobilize to stop the fire’s spread, government spokesman Anucha Burapachaisri said.

He added that Prayuth ordered officials to watch for anyone deliberately lighting fires to clear land for farming and other purposes, a practice that has been blamed for past fires. The cause of the fire in Nakhon Nayok was not yet clear, though some local media reports said it was set off by lightning.

Bancha was quoted by Thai Rath as saying a storm on Tuesday ignited a fire nearby that strong winds blew to the Khao Laem area.

Separate forest fires have been raging farther north, Anucha noted, including in Chiang Mai province, where water was dumped from the air Wednesday in an effort the dowse the flames.