The central train station in Tunis was on fire early Saturday just hours after long-time President Zine el-Abidine Ben Ali left the country, dpa reported.
Prime Minister Mohamed Ghannouchi, who announced he would serve as president, described the situation as complete security chaos. He called on residents to join forces to protect their belongings.
Supermarkets had also been set ablaze and witnesses described plundering and helicopters flying over the city with spotlights.
Late Friday, shots were heard in the city centre, but had fallen silent in the early hours of Saturday.
Ben Ali left the country on Friday after a month-long popular revolt that claimed dozens of lives. He had fired his government and announced early elections before leaving. His whereabouts were unknown early Saturday.
A state of emergency was declared in Tunisia on Friday evening. The army took control of the main airport in Tunis and Tunisian airspace was closed.