The Middle East is seeing a wave of pro-democracy protest, fuelled by the fall of Egypt's Hosni Mubarak on 11 February, and long-time Tunisian President Zine al-Abidine Ben Ali in January.
On Monday, reports from Tripoli suggested the streets were mainly quiet, with government forces still patrolling Green Square after crushing protests in what witnesses called a "massacre".
On Sunday evening, witnesses spoke of tear gas and live ammunition being used against protesters by the security forces.
A man who attended a rally in Tripoli's central Green Square said snipers on rooftops had fired indiscriminately into the crowd using what sounded like machine guns.
He also said, "People were shot in the head and in the back. I've now taken refuge in my home. I'm afraid to leave. There is a climate of fear," he told the BBC.
Other reports say gunmen in vehicles with photos of Col. Gaddafi sped through the streets, opening fire and running people over.
A central government building, the People's Hall, was said to have been set ablaze and firefighters were trying to put out the flames.
Libyan leader Muammar Gaddafi's son, Saif al-Islam Gaddafi, has warned that civil war could hit the country.
His comments came in a lengthy TV address as anti-government protests spread to the capital Tripoli and were brutally countered by security forces.