Amateur footage of the incident. 15.01.15'
At least two people were killed when Belgian counter-terrorist police raided an apartment used by Islamist radicals.
Local media said, describing a coordinated, national operation related to last week's attacks in Paris.
Judiciary officials confirmed only that a counter-terrorism operation took place near the centre of Verviers, a town in the east of the country between the city of Liege and the German border.
Public radio RTBF, which reported a number of other police actions in and around Brussels, said there were no casualties among the security forces. Two unidentified people were killed and a third seriously wounded. Several others were detained.
Earlier, prosecutors said they had detained a man in Belgium whom they suspected of supplying weaponry to Amedy Coulibaly, killer of four people at a Paris Jewish grocery last week.
In a report that could not be immediately confirmed, the Web site of La Meuse newspaper quoted an unidentified police officer saying: "We've averted a Belgian Charlie Hebdo."
Two French brothers, who like Coulibaly claimed allegiance to Islamists militants in the Middle East, killed 12 people last Wednesday, Jan. 7, at the Paris offices of satirical newspaper Charlie Hebdo.
RTBF said Thursday's operation in Verviers was intended to check on suspected radicals one of several being conducted across the country against people believed to have returned to Belgium after taking part in the Syrian civil war.
Belgium has seen significant radical Islamist activity among its Muslim population. RTBF said police raids were also under way in Brussels.
Belga news agency said police were hunting a man who witnesses said had brandished a weapon and shouted religious slogans in Arabic at a Brussels metro station.
Local media said gunshots and several explosions were heard on a residential street in Verviers near the railway station and one photo posted by a witness on Twitter showed police vehicles and ambulances blocking the street.
Police had raided an apartment above the Croissant d'Or bakery, RTBF said.
The channel showed video of a building at night lit up by flames, with the sound of shots being fired. A local resident named Marie-Laure told RTBF said she was in the street with her children when a police commando told them to run for cover.
"When we began running, we heard three or four big explosions and shots," she said. "It was really startling."
Per head of population, Belgium is the European country from where the highest number of citizens have taken part in fighting for Syrian rebels in the past four years, data compiled by security researchers have shown.
A court in Antwerp is due to deliver its verdict on 46 people accused of recruiting young men to join jihadists or of becoming jihadists in Syria, Belgium's largest Islamist militant trial to date.
The court was to have given its verdict this week, but it was delayed for a month after the Paris violence.