At least one person was reportedly killed and two were seriously injured, according to the Associated Press.
The explosion partially destroyed the building located on Rue de Chalon.
The official cause of the explosion is unknown, but an official with Belgium's Crisis Center said "It is probably a gas explosion," according to Reuters, adding that there was no indication of it being a militant attack.
Emergency services and rescue workers are working at the site, Breaking 911 reports.
The spokesman, who was not named, said that more people were believed to be trapped under the rubble, the AP reported.
Chimay is located in the province of Hainaut, near the border with France and about 75 miles south of Brussels, the AP reported.
#BREAKING: Massive explosion reported at sports stadium in #Chimay,#Belgium, according to local media. More to come.
- Al Boe (@AlBoeNEWS) August 25, 2016
#Belgium #Chimay - Not saying it's terrorism, but: loud explosion in a sports complex. Half of it came down. Fatalities are to be expected.
- Terror Events (@TerrorEvents) August 25, 2016This story is developing. Check back or refresh this page for updates.