This weekend's clashes come as Lebanese politicians continue to struggle to agree a new government.
Clashes between police and demonstrators broke out in downtown Beirut after some protesters started throwing stones at police near the parliament building.
The pitched battles across the area of Beirut that was a frontline of the country's 15-year civil war lasted about nine hours, spilling on to the steps and into the courtyard of a prominent mosque, inside which some protesters had sought refuge.
More street rallies were expected later Sunday as part of the wave of popular protests that has demanded the wholesale ouster of the Lebanese political class, which the activists condemn as inept and corrupt.
The Red Cross said it had rushed 80 people to city hospitals while 140, including both protesters and members of the security forces, were given first aid at the scene of the clashes.
"There was no justification for the brutal use of force unleashed by Lebanon's riot police against largely peaceful demonstrators in downtown Beirut", said Michael Page, deputy Middle East director at HRW. Then prime minister Saad Hariri resigned in late October to take responsibility for the protests.
But before they all converged near the road leading to parliament, dozens of protesters flung rocks and plant pots filled with earth at the police guarding the institution, local television channels showed.
Amid a downpour of rain and the advance of security forces, protesters retreated and the situation calmed in central Beirut.
At least 377 people were injured in Saturday's clashes, according to the Red Cross and the Lebanese Civil Defense.
Parts of central Beirut were choked in teargas and swarmed by riot police as street battles raged for almost nine hours, with protesters throwing flares, stones and branches at security forces.
"Form a government and pave the way towards political and economic solutions", he said. Workers also welded fencing together across roadways that lead to Parliament to make it harder for demonstrators to push through. The economy has seen no growth and flows of foreign currency dried up in the already heavily indebted country that relies on imports for most basic goods.
Earlier in Beirut on Sunday, shopkeepers, banks and other businesses swept up broken glass and boarded-up windows.
Banks have also imposed strict controls on foreign transfers and the withdrawal of U.S. dollars.
Protesters have also turned their anger on the banks - which have curbed access to savings - with some smashing the facade of the banking association on Saturday night.
Political factions agreed on December 19 to appoint former education minister Hassan Diab as the new premier but have since squabbled over proposed ministers.
Nearby soot and ashes still littered the ground where security forces burned the tents of the protesters' sit-in during the chaotic melee.