Belgium's parliament, universities, and scientific institutions have been targeted in a coordinated cyberattack.
Belnet, the company that provides internet services to the country's government agencies, said their network was "victim of a large-scale attack" on Tuesday.
Unknown hackers committed a distributed denial of service (DDoS) attack at 11:00 (CEST), Belnet said, designed to prevent the availability of certain online services by overloading servers with data.
Belnet said the attack did not breach or steal any information from the network.
However, the hack meant all of Belnet's customers were either completely or partially cut off from the internet.
Belgian citizens were unable to access the websites of certain administrations on Tuesday and students could not use their university's online services.
The country's federal parliament has been forced to cancel several committees due to the issue, while online reservation systems for vaccination centres were also temporarily down.
"About 200 organisations were affected, including universities, public administrations, and research institutes," Belnet said in a statement.
"We are fully aware of the impact on the organisations connected to our network and their users and we are aware that this has had a profound impact on their operations," the company's Technical Director Dirk Haex added.
Belnet said the hack had been brought under control by Tuesday evening.
"Belnet immediately activated its crisis procedures and contacted the Centre for Cybersecurity Belgium (CCB) to bring the attack under control," the company statement said.
"Belnet's teams continue to monitor the situation minute by minute."
The perpetrators of the cyberattack have not yet been identified but Belnet believes that the hack only aimed to "saturate" their network.
"There is no indication that the cybercriminals infiltrated any network," the company reported, adding that they had filed a complaint with the Federal Computer Crime Unit.
"Belnet continually invests in cybersecurity," said Haex, "however, yesterday's DDoS attack was of such a scale that our entire network was saturated."
"The fact that the perpetrators constantly changed their tactics made it even more difficult to neutralise the attack."