Witnesses in Sousse say security forces fired tear gas to disperse hundreds of angry protesters blocking roads.
Violent protests have broken out in at least six Tunisian cities, including the capital Tunis and the coastal city of Sousse, as anger mounts over economic hardship.
The demonstrations on Saturday night come as Tunisia marks the tenth anniversary of the revolution that toppled late president Zine El Abidine Ben Ali and sparked the Arab Spring uprisings.
The protests pose a challenge for the government of Hicham Mechichi, who earlier reshuffled the cabinet with new ministers including the ministries of interior, justice and energy.
Witnesses in Sousse said security forces fired tear gas to disperse hundreds of angry protesters who were blocking roads and burning tyres.
Security sources said young men in Sousse broke into shops. Clashes took place in the city of Kalaa Kebira near Sousse.
A decade after the revolution against widespread unemployment, poverty, corruption and injustice, Tunisia made smooth progress towards democracy, but its economic situation worsened with poor public services and the country on the verge of bankruptcy.
Violent protests also took place in several parts of the capital, including Ettadamen, Mallassin and Fouchana and Sijoumi.
There were also night protests and riots in Kef, Bizerte and Siliana, in the north of the country.