The doctor is alleged to have falsified vaccine certificates to help people avoid COVID-19 restrictions.
A doctor has been accused of registering 2,000 false COVID-19 vaccinations in the Belgian region of Wallonia.
The practitioner -- who has not been identified -- faces charges of forgery and false documentation and is under investigation.
Authorities allege he falsified people's vaccine status to help them avoid coronavirus-related restrictions.
Wallonia's health minister Christie Morreale has described it as the "most serious" instance of fraud in Belgium during the pandemic.
The doctor is alleged to have offered his services "to the four corners of Wallonia", a French-speaking region in southern Belgium.
On some occasions, he was reportedly paid for falsely certifying that patients had been vaccinated.
The alleged fraud was discovered when the Wallonia Agency for Quality Living noticed that the same doctor had issued two COVID-19 certificates at the same time in different places.
Morreale told RTBF that it was impossible for a single doctor to vaccinate 2,000 people in so many different areas.
"We realised that on anti-vax websites there were calls to buy false certificates," she said, "It's a vaccination fraud by a doctor who encoded an astronomical number of people."
The investigation has been referred to Belgian courts and the country's medical association. The doctor has since been removed from the database that validates COVID-19 vaccines.
Morreale has said that those people who benefitted from his fraud are also liable for prosecution.
The regional health minister said that the patients' COVID-19 certificates have been "suspended" and they will be offered a proper vaccination.
"This is the most important and serious anomaly, it is an extremely dangerous act ... a breach of trust," Morreale said.
Currently, 75% of Belgian adults have been fully vaccinated against the virus, but the country has recorded a severe rise in infections in recent days.
On Sunday, police clashed with so-called "freedom" demonstrators at a rally against increased health restrictions.