(CNN)Authorities in Belgium are still hunting for a far-right extremist who had threatened one of the country's top doctors and had a rocket launcher in his car.
The man, identified by police as 46-year-old former soldier Jurgen Conings, was last seen after leaving for work on Monday. Officers describe him as being 1.80 meters (5 feet 11 inches) tall, with a muscular build.
An initial investigation found that he could be a threat to certain institutions or people, the Belgian Federal Prosecutor's Office said in a Wednesday statement.
The manhunt entered its third day on Thursday, with 250 police officers and 150 service members from the Belgian army combing through the Hoge Kempen National Park, close to the border with the Netherlands.
Among those who could be under threat is Marc Van Ranst, one of Belgium's top virologists. Speaking to CNN on Wednesday, Van Ranst said Conings had threatened him on social media, something he said was "almost a daily event."
Van Ranst and other prominent Belgian doctors have been receiving police protection since last July, when they first started receiving threats from far-right extremists, unhappy with restrictions to fight the coronavirus.
"On Tuesday morning, it emerged that man, a trained soldier, was in possession of weapons," the prosecutor's statement read. "Those elements, along with certain personal personality traits and his proficiency with firearms, prompted the authorities to take the facts seriously."
Authorities have since found the suspect's car, an SUV, close to the Hoge Kempen National Park.
"Inside the vehicle, authorities discovered four Law anti-tank rocket launchers and ammunition," the prosecutor said.
Authorities believe Conings is also armed with a machine gun, a spokesman for the Belgian Federal Prosecutor's Office, Eric Van Duyse, told CNN Thursday.
The suspect is presumed to be hiding among the 12,000 hectares of parkland, the spokesman said.
Conings suddenly disappeared on Monday leaving a letter in his house where he claimed he would do something that "would change society forever," Van Duyse told CNN. "He said society would not be the same, though it's unclear what he meant by that."
In the letter, Conings also hinted he would not be coming back, Van Duyse added.
'They whisked me from my hospital'
Van Ranst said he and his family were placed under protective custody and taken to a secure location by Belgian authorities on Tuesday, after the manhunt was launched.
"My son and wife were picked up at their school and work," he said. "Then they whisked me from my hospital."
When asked how he felt about his current situation, Van Ranst said: "It's not something I'm not accustomed to, because we receive threats almost on a daily basis, but hearing that he had a rocket launcher gets you a little bit worried."
The Belgium's National Crisis Center (OCAM) has raised the threat level with regards to Conings to a level four, but kept the overall national terror threat level at two. Authorities have advised people to report any sightings, but to avoid engaging with him.
Speaking to CNN affiliate VTM on Tuesday, Belgian Justice Minister Vincent Van Quickenborn said Conings was known to the country's security services.
"He is on the terrorist list because of right-wing extremist sympathies," Van Quickenborn said. "There are also indications that he ... that he is violent. And in the past 24 hours, concrete indications have emerged that there is an acute threat from that man."
"That is why the services have left nothing to chance," he added.