A third night of unrest has shaken Tunisia where authorities on Thursday said more than 600 people have been arrested this week as anger at austerity measures boils over on the streets.

Tunisia is considered a rare success story of the Arab Spring uprisings that began in the North African country in 2011 and spread across the region, toppling autocrats.

But the authorities have failed to resolve the issues of poverty and unemployment.

Police detained 328 people on Wednesday for theft, looting, arson and blocking roads, the interior ministry said, after arresting more than 280 people over the previous two days.

The latest unrest saw a provincial police station torched, Molotov cocktails hurled at police and tear gas fired, but ministry spokesman Khalifa Chibani said the “violence” was less intense than in previous days.

Twenty-one members of the security forces were injured, Chibani said. There was no immediate toll available for any casualties among the protesters.

Tunisia is often seen as having had a relatively smooth transition since the 2011 uprising that toppled longtime dictator Zine El Abidine Ben Ali.

But Tunisians have expressed frustration since the start of the year over austerity measures expected to further increase prices in a struggling economy.

The North African country introduced hikes in value-added tax and social contributions as part of a tough new budget.

Political scientist Olfa Lamloum called the measures “the straw that breaks the camel's back”.

“Young people are disappointed with the revolution, especially because of the high cost of living,” she said.

Lamloum pointed to “deepening social inequalities” highlighted by official figures showing rising poverty, unemployment and illiteracy particularly among young people.

'Nostalgia for strong state'

Conflict analysts International Crisis Group (ICG) warned the country's political class on Thursday against succumbing to “authoritarian temptation”.

While politicians had so far resisted the urge to backtrack on reforms, ICG said “in the context of an economic slump, the nostalgia for a strong state, like the one that the former regime claimed to defend, is spreading”.

The recent unrest started with peaceful protests against the measures last week, but escalated into clashes with police in the night of Monday to Tuesday.

In a third night of clashes, unrest hit several areas across the country including the central city of Kasserine, and the northern towns of Siliana, Tebourba and Thala.

In Siliana, youths threw stones and Molotov cocktails at security forces. Police responded with tear gas, an AFP correspondent said.

Scuffles also broke out in some Tunis neighbourhoods.

Youths in Kasserine tried to block roads with burning tyres and hurled stones at members of the police force, another AFP correspondent said.

In Tebourba, where a man died during unrest in the night of Monday to Tuesday, police fired tear gas after dozens of protesters took to the streets, according to a resident.

The main police station in the northern town of Thala was set on fire, Chibani said.

Activists campaigning against the austerity measures have called for a massive protest on Friday.

During a visit Wednesday to a town near Tebourba, Prime Minister Youssef Chahed condemned what he called acts of vandalism. “Whenever there is social friction in Tunisia, the vandals come out,” he said.

The Popular Front, an opposition party accused by the government of supporting the rioters, urged Chahed to “find solutions for young Tunisians”.

“Peaceful demonstrations are part of the democratic equation, but damaging public property and harming citizens is illegal,” said Hamma Hammami, spokesman for the leftist party.

Protests are common in the North African state in the month of January, when Tunisians mark the anniversary of the 2011 revolution.

The uprising began in December 2010 after street vendor Mohamed Bouazizi set himself on fire and later died in a protest over unemployment and police harassment.

January 2016 saw the biggest wave of public discontent since the uprising as the death of a jobless protester in Kasserine sparked days of unrest.