Demonstrators yelling "Down with communism!" smashed their way into the interim government's headquarters with rocks and steel rods Sunday in the most violent protest since the December revolution.
Soldiers fell back before the demonstrators, who numbered more than 1,000. An official said not enough troops were on hand to keep order.
The state news agency Rompres said more than 20 paratroopers were severely wounded, but reporters saw only two injured soldiers.
The building on Victory Square has been used by Prime Minister Petre Roman since the revolution that toppled longtime Communist dictator Nicolae Ceausescu, later executed along with his wife, Elena.
The enraged crowd ransacked offices, shouting for interim President Ion Iliescu to resign and accusing the provisional government of being dominated by Communists from the Ceausescu regime.
The only member of government in the building apparently was Deputy Prime Minister Gelu Voican Voiculescu.
Demonstrators seized him, punched him and dragged him onto a balcony, where he was jeered. Soldiers hustled him to his office, where they guarded him from hundreds of demonstrators yelling "Voican! Voican!"
The crowd broke inside the building after soldiers hauled away protesters who scaled the building and waved Romanian flags from a balcony.
Protesters told the crowd one man who was hauled away had been shot, prompting cries of "Assassins! Murderers!"
More than 1,000 people in front of the building cheered as protesters smashed the windows and glass doors. About 500 people poured in.
Authorities later sent infantry reinforcements, who kept demonstrators from entering the building. All protesters were finally ousted, but the crowd outside grew to more than 5,000, more than half merely curious onlookers.
No trouble was reported elsewhere in the city or in the country.
Prime Minister Roman, who was in Paris on a four-day official visit, said the protesters represented an insignificant portion of the population. He told French TV that he had spoken with officials of the ruling Provisional Council for National Unity who assured him that "All is in order."
"At this time we are only a provisional council," Roman said. "We do not have a real legitimacy, but these 500 persons that entered the building of the provisional government, they represent nothing."
He told French journalists earlier Sunday that his Eastern European nation had reached political stability under the leadership of Iliescu.