Uprising could bring the death of Lebanese political system where power is shared among religious groups, analysts say.
Sunday morning’s violence around the epicentre of the protest site in Beirut was some of the worst since the demonstrations began two months ago.
Clashes brought the central area to a standstill for more than eight hours as security forces fired a stream of tear gas canisters at hundreds of protesters, who set fires in rubbish bins on the main streets, in part to mitigate the effects of the gas.
The Red Cross and the Lebanese Civil Defence said at least 46 people were injured and transported to hospitals. More protests are expected later on Sunday.
The protesters chanted slogans against security forces and government officials and pelted police with stones in scenes not seen in the capital since the demonstrations began on October 17.
At one point, the scuffles reached the headquarters of one of the main Lebanese political parties, the Kataeb, where many protesters were taking cover.
Samy Gemayel, the head of the Kataeb, appeared on local TV stations as he tried to separate the protesters from advancing security forces.
Lebanon is facing one of its worst economic crises in decades, and the protesters accuse the ruling political class in place for 30 years of mismanagement and corruption.
The violence comes just two days before the president holds talks with different parliamentary blocs to name a new prime minister.
The government headed by former Prime Minister Saad Hariri resigned on October 29, two weeks after the nationwide protests began.
Political groups have been unable to agree on a new candidate while protesters have called for a government unaffiliated with established political parties.
Local TV station LBC showed dozens chanting against Hariri, who has emerged as the favourite candidate despite all the political bickering.
The protesters also chanted: “The people want to bring down the regime.” They accused government forces of excessive force.
The trouble started on Saturday when dozens of men, some wearing masks, threw stones and firecrackers at security forces on one edge of the protest camp in central Beirut.
They were supporters of the Shia Hezbollah and Amal groups, angered by some of the criticism of their leaders by anti-government protesters.
It was the second time this week the groups tried to attack the protest camp.
The National News Agency said one member of security forces was injured. Local leaders, including a mosque preacher, appealed for calm.
Hours later, hundreds of anti-government protesters, including women, gathered outside Parliament, hundreds of metres away from the protest camp.
Chaos ensued with reports of an attack on the anti-government rally, leading to a confrontation with security forces who tried to disperse the protesters.
For the first time since the protests erupted in Beirut, anti-riot police fired rubber-coated bullets as they chased the demonstrators away from the area.
It was not clear what caused the crackdown. The parliament speaker is the head of the Shia Amal group.
The clashes spread to streets surrounding the protest camp, engulfing the area in thick, white smoke and the odour of tear gas.
Security forces chased protesters around central Beirut, some firing rubber bullets and several volleys of tear gas from armoured vehicles.
Dozens of protesters had travelled to Beirut from the northern city of Tripoli to take part in the rally outside the parliament building.
The National News Agency reported some shop windows in the commercial part of central Beirut were smashed by vandals.
One officer was injured in the eye when a protester hit him with a stone, according to an Associated Press reporter.
Early on Sunday, nearly a dozen riot police stood over two protesters and beat them with batons. The two were later taken away to be treated by medics.
Tension has been building in the protest camp. Some accused activists who organise discussions in the camp under the name “the Hub” of hosting critics of Hezbollah and calling for normalisation of ties with Israel.
The tent was attacked earlier in the week with firecrackers, burning it down. On Saturday, a rally to support the Hub was cancelled shortly before the attempted attack on the protest camp.