No one has been injured and by lunchtime the situation was back under control.
The gas leak was near to the main entrance of the school and is believed to have been caused by drilling work in the cellar of an adjacent house.
As well as workers from Sibelga, the Brussels Fire Service also attended the scene. The pupils and staff from were evacuated via the back entrance of the school. A crèche that is housed in the same building was also evacuated.