In Tunis thousands of people flooded the central Habib Bourguiba Avenue, close to the tree-lined boulevard, where violent anti-government protests were raging two years ago, when the so-called Arab Sprig was ignited.
Flocking to the Interior Ministry office, protesters were chanting "The people want the fall of the regime!"
Security forces cordoned off the area.
As an ambulance carrying Belaid's body was driven in front of the ministry, hundreds of mourners crowded around the vehicle.
Calls for a second revolution were heard from the crowd. The protesters were chanting “We are all Chokri,” “O Chokri, O martyr, we will follow your path," and “Terrorism, bullets, Tunisians are fearless”.
Police responded to mass gathering in Tunis with teargas and warning shots. There have also been reports that an ambulance was teargased.
Further protests have erupted in more than 12 towns and cities across Tunisia.