A house close to a restaurant in the city of Bastogne, near the Luxembourg border, exploded just before 9pm (8pm BST).
Benoît Lutgen, the city’s mayor, said two people were seriously injured, while three others had less severe injuries.
A severely wounded person was taken to hospital by helicopter which landed nearby.
One witness, Olivier, said: “There are several blood wounded along the road, a scene of horror.”
A host of emergency services vehicles were rushed to the scene in Rue Joseph-Renquin as the mayor triggered the communal emergency plan.
Mr Lugen, added: “The house where the explosion took place was completely blown up and there is also damage to neighbouring houses.”
One person was intially reported as missing, but was later found nearby.
Another witness, said: “The emergency vehicles of the various neighbouring towns are on the scene.
“We do not yet know the real circumstances of this tragedy.
“The shops and houses nearby are damaged by the violence of the explosion.”
After firefighters attended the scene and searched under the rubble left by the explosion, they came to the conclusion a gas leak was the cause.
A Bastogne Fire spokesman, said: “There is no fire following the explosion and the helicopter landed at about 10.15pm to take a seriously wounded person to hospital.”
Belgium has been on high alert for terror attacks following three Islamic State (ISIS) co-ordinated suicide bombings in March last year.
Two bombs at Brussels Airport and one at Maalbeek metro station in central Brussels killed 32 civilians and injured more than 300 people.
Another bomb was also found during a search of the airport.
Belgium’s latest terror attack occured on Friday in Brussels after a Somali man attacked two soldiers patrolling in central Brussels with a knife.
The man rushed towards them and attacked them from behind while shouting “Allahu Akbar” (God is great), the Belgian Federal Prosecutor’s Office said.
One of the soldiers opened fire and hit the attacker twice, who later died in hospital from his injuries.
He was found with a replica firearm and two copies of the Korean on his body.
This is a breaking story.
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