A container of picric acid was found on Tuesday in a former laboratory near the centre of Mouscron, prompting a controlled explosion by bomb disposal experts.
Local authorities said the discovery was made in an old laboratory building on Rue de la Station.
As picric acid can become highly explosive over time, specialist services were called in as a precaution to handle the chemical under the safest possible conditions.
The bomb disposal unit later destroyed the substance in a controlled blast.
Residents of the Cité de la Main district and nearby areas may have heard a loud bang, authorities said around midday, but stressed that all necessary safety measures had been taken and that the situation was under control.
