Amid reports of looting and gunfire, soldiers and tanks have been stationed in the capital Tunis to restore order and enforce a state of emergency, including a dusk-to-dawn curfew.
Dozens of inmates are reported to have been killed in breakouts at two prisons, with the Tunisian official news agency reporting 42 dead in a riot and fire at a prison at Monastir.
Ben Ali and his family arrived in Saudi Arabia on January 15 after fleeing Tunisia amid violent protests over his 23 years in power.
Speaker of parliament Fouad Mebazza has been sworn in as interim president and has called for the formation of a new coalition government.
Authorities say that under the constitution, a presidential election should be held within 60 days.
Many in Tunisia blame the 74-year-old Ben Ali and his entourage for the corruption, unemployment, and political repression that have plagued the small nation for much of his rule.
Thousands gathered in Tunis on January 14 to demand his resignation, despite his promise to introduce new freedoms and step down after his sixth term in office expires in 2014.
The wave of protest was sparked by the suicide of a 26-year-old unemployed graduate who set himself on fire in mid-December to protest the confiscation of his license to sell fruits and vegetables.
The protests started in the provinces but this week reached the capital as well as several of Tunisia's popular beach resorts.
Some human rights group say almost 70 have been killed in the unrest, about three times the official toll.
World leaders urged for restraint following Ben Ali's departure and called on the country's interim leaders to steer the country toward free and fair elections.
U.S. President Barack Obama has hailed the "courage" and "dignity" of protesters and called for swift elections.
French President Nicolas Sarkozy, who barred Ben Ali from seeking refuge in his country -- Tunisia's former colonial ruler -- has called an emergency meeting on Tunisia with senior ministers.
German Chancellor Angela Merkel said her government would be closely monitoring events in Tunisia.
"The situation in Tunisia is very serious and it became clear that the standstill in the country made people very restless," Merkel said. "We will closely monitor the situation and take care of those Germans who are still in Tunisia. The foreign ministry is the point of contact for all Germans who have queries."
Meanwhile, the first tourists from Germany, Britain, and Belgium were being repatriated from Tunisia.
Fearing more violence, British tour operator Thomas Cook has started evacuating thousands of tourists from the country.
British holidaymakers returning to Manchester voiced both frustration and relief.
"The whole thing was an absolute nightmare, actually," one told Reuters. "We wouldn't have gone in the first place if we had known trouble was going on there."
"I was scared. I was very scared," said another. "Now I'm glad I'm home, safe."
Tunisian air space, closed on January 14, has reportedly been reopened as well as all Tunisian airports.
compiled from Reuters and agency reports