The blaze in the High Fens, a nature reserve in the east of the country, has been burning since Friday and firefighters from across Belgium and neighbouring Germany and Luxembourg have sought to contain it, as have the army and farmers.
By early Sunday AEST, it had burned 2700ha, the office of the governor of Liege said, indicating the fire was spreading, having increased from 1600 hectares earlier in the day.
That makes the fire by far the biggest on record in Belgium — nearly double the size of a blaze in 2011 that burned close to 1400ha, data from the European Forest Fire Information System showed.
Local authorities asked residents of several villages to evacuate their homes as a precaution on Saturday, due to changing winds and smoke in the area. Tourists staying in the area were advised to leave, while a children's summer camp was also evacuated, Belgian Defence Minister Theo Francken said in a post on X.
The terrain of the nature reserve was making it difficult for emergency services to attack the fire at close range using their usual resources, the Liege governor's office noted.
European countries including Belgium suffered their fifth heatwave of the summer this week. Scientists say human-caused climate change has increased the likelihood of the hot and dry conditions that allow wildfires to spread faster and burn longer.
The EU co-ordinates the deployment of extra resources pooled from European countries, when a country requests emergency help.
The aircraft sent to Belgium on Saturday were from the Czech Republic, Sweden and the Netherlands, EU Crisis Commissioner Hadja Lahbib said in a post on X.
Meanwhile, local officials said 650 residents evacuated their homes as a wildfire burned in Landes, south-western France.
The fire began on Thursday and, according to authorities, reignited on Saturday - with more than 500 firefighters deployed to tackle the blaze.
