Firefighters were still battling the blaze in the High Fens (Hautes Fagnes) on Sunday, as strong winds, difficult terrain and poor visibility hampered efforts despite major air support.
According to unconfirmed figures, about 3,000 hectares have already been destroyed by the fire.
The changing wind and the limited access for ground crews have made the operation particularly difficult.
However, firefighters can now rely on substantial support from the air.
Two Dutch military twin-rotor Boeing CH-47 Chinook helicopters arrived in the area on Saturday. Each can drop up to 7,000 litres of water.
They are reinforcing the two smaller MD902 helicopters from the Belgian Federal Police, which have been involved since the early hours of the fire.
Two Saab AT-802 water-bombing aircraft from the European strategic reserve are also now operating at the scene, European Commissioner for Crisis Management Hadja Lahbib said on Sunday.
The aircraft, nicknamed “Air Boss,” can each carry 3,000 litres of water.
Heavy smoke, however, reduced visibility in the air on Sunday.
To prevent any collision between aircraft involved in the operation, as happened recently in Greece, the European crisis centre has sent a liaison officer to the area.
The officer has proposed applying the same flight safety rules for water bombers as those used in southern Europe, which has also been hit by major forest fires this summer.
