The largest fire in Belgium's history is spreading toward the German border, as hundreds of firefighters try to contain the blaze, which has already engulfed 3000 hectares, The Telegraph reports.

The fire has doubled in size in the past 24 hours, and is located just three kilometers from Germany. The blaze, which started on Friday, has engulfed the Hohes Venn nature reserve in the east of the country. Firefighters from Germany, Luxembourg, and other EU countries have arrived to assist Belgian firefighters.

Regional authorities warned on Sunday morning that the situation in the park remained precarious. Around 600 residents of nearby municipalities in the province of Liège, which borders Germany, were evacuated on Saturday due to thick smoke enveloping their homes.

In the German city of Monschau, authorities reported Sunday night that the fire had come within about three kilometers of the border and advised residents of outlying areas to consider temporary evacuation due to health risks associated with smoke.

Firefighting efforts are hampered by unstable winds and terrain features—peat bogs, heather, and wooden platforms—that pose a risk of heavy equipment getting stuck and make it difficult for firefighters to reach the fire. However, rescuers say a cooler weather forecast could help bring the situation under control.

On Sunday evening, air reinforcements from the Czech Republic and Sweden were due to join the operation – in addition to Belgian Federal Police helicopters and Dutch aircraft – thanks to Belgium's activation of the EU's civil protection mechanism.

Like much of Europe, Belgium has been hit by a new wave of heat and drought in recent days, with temperatures reaching 37 degrees Celsius in some parts of the country on Friday.

Since the beginning of the month, a series of severe fires caused by a series of heat waves have forced evacuations in Germany, France, the UK, Croatia and Greece.