Offices of the Association of Lebanese Banks were also trashed during the protests.
The scene in Beirut is one of the increasingly angry demonstrations as Lebanese citizens express their frustration and fury over its government’s negligence in this week’s devastating explosion.
Protesters have called for their politicians to resign and be punished for turning a blind eye that led to Tuesday’s blast — the biggest to ever hit Beirut.
Around 158 casualties and 6,000 injuries result from the Beirut explosion have so far been reported, compounding months of political and economic meltdown.
A policeman was killed during the clashes, a spokesman said. A policeman at the scene said the officer died when he fell into an elevator shaft in a nearby building after being chased by protesters.
The Red Cross said it had treated 117 people for injuries on the scene while another 55 were taken to hospital.
Policemen wounded by stones were treated by ambulance workers. A fire broke out in central Martyrs' Square.
Dozens of protesters broke into the foreign ministry where they burnt a portrait of President Michel Aoun, a representative for many of a political class that has ruled Lebanon for decades and that they say is to blame for its current mess.
"We are staying here. We call on the Lebanese people to occupy all the ministries," a demonstrator said by megaphone.
About 10,000 people gathered in Martyrs' Square, some throwing stones. Police fired tear gas when some protesters tried to break through the barrier blocking a street leading to parliament, a Reuters journalist said.
Police confirmed shots and rubber bullets had been fired. It was not immediately clear who fired the shots.
Riot police shot dozens of teargas canisters at protesters, who hit back with firecrackers and stones.