Security has been stepped up in centre of the Tunisian capital, a day after President Zine al-Abidine Ben Ali stepped aside following his failure to quell the worst anti-government unrest in his two decades in power.
Hundreds of troops are patrolling Tunis and a state of emergency is in force, the BBC reports.
There were scenes of looting overnight in several areas, witnesses said.
The main thoroughfare in Tunis, Avenue Bourguiba, was blocked off by troops after the lifting of an overnight curfew.
In a television address in Tunis, Prime Minister Mohamed Ghannouchi said he had taken over as interim president, and vowed to respect the constitution and restore stability.
Mr Ghannouchi said he would hold talks with opposition groups to try to form a unity government.
Earlier on Friday, Mr Ben Ali had dismissed his government and dissolved parliament, and called new elections within six months.
He had declared a state of emergency and said protesters would be shot in an increasingly violent confrontation.
Doctors are quoted as sayingas many as 13 people were killed in overnight clashes in the capital Tunis where thousands had rallied, demanding the immediate resignation of Mr Ben Ali.
The protesters were not satisifed with an announcement by the president on Thursday that he would step down in 2014, and instead called for him to leave office immediately.
Security forces in the capital, Tunis, are said to have opened fire to control the crowd.
Thousands of British and German tourists are being evacuated from the country.