At least 50,000 people turned out yesterday to honour Mr Belaid in his home district of Jebel al Jaloud in the capital, chanting anti-Islamist and anti-government slogans. It was Tunisia's biggest funeral since the death of Habib Bourguiba, independence leader and the country's first president, in 2000.
Violence erupted near the cemetery as police fired teargas at demonstrators who threw stones and set cars ablaze. Police also used teargas against protesters near the Interior Ministry, a frequent flashpoint for clashes in the Tunisian capital.
Tunisia, cradle of the Arab uprisings, is riven by tensions between dominant Islamists and their secular opponents, and by frustration at the lack of social and economic progress since President Zine al Abidine Ben Ali was ousted in January 2011.
Mr Belaid's assassination has shocked a country which had hitherto experienced a relatively peaceful political transition.
"The people want a new revolution," shouted mourners, who also sang the national anthem. Crowds surged around an open army lorry carrying Mr Belaid's coffin, draped in a Tunisian flag, from a cultural centre in Jebel al Jaloud towards the Jallaz cemetery, as a security forces helicopter flew overhead.
"Belaid, rest in peace, we will continue the struggle," mourners chanted, holding portraits of the politician killed near his home on Wednesday by a gunman who fled on a motorcycle.
Some demonstrators denounced Rachid Ghannouchi, leader of the ruling Islamist Ennahda party. "Ghannouchi, assassin, criminal," they chanted. "Tunisia is free, terrorism out."
Police fired teargas to disperse anti-government protesters throwing stones and petrol bombs in the southern mining town of Gafsa, a stronghold of support for Mr Belaid. Crowds there had chanted: "The people want the fall of the regime", a slogan first used against Mr Ben Ali.
In Sidi Bouzid, the southern town where the revolt against the ousted president began, about 10,000 marched to mourn Mr Belaid and shout slogans against Ennahda and the government.
Banks, factories and some shops were closed in Tunis and other cities in response to a strike called by unions in protest at Mr Belaid's killing, but buses were running normally. Tunis Air suspended all its flights because of the strikes. Airport sources in Cairo said EgyptAir had cancelled two flights to Tunisia after staff at Tunis airport joined the general strike.
After Mr Belaid's assassination, Prime Minister Hamdi Jebali, an Islamist, said he would dissolve the government and form a cabinet of technocrats to rule until elections could be held. However, his own Ennahda party and its secular coalition partners complained they had not been consulted, casting doubt over the status of the government and compounding political uncertainty. No-one has claimed responsibility for the killing of Mr Belaid, who was a lawyer. His family have blamed Ennahda but the party has denied any hand in the assassination. Crowds have attacked several Ennahda party offices in Tunis and other cities in the past two days.
While Mr Belaid had only a modest political following, his criticism of Ennahda policies spoke for many Tunisians who fear religious radicals are bent on snuffing out freedoms won in the first of the revolts that rippled through the Arab world.