Thousands of supporters of a hardline secularist Tunisian party protested on Sunday against President Kais Saied for his march towards one-man rule and failure to avert an economic crisis, showing the increasingly broad opposition to his actions.

The protest is the biggest by the Free Constitutional Party since Saied seized executive power last summer, dismissing parliament and saying he could rule by decree in moves that many of his rivals have called a coup.

However, the party and its fiery leader Abir Moussi are no stalwarts of the democratic system Tunisia introduced after its 2011 revolution, pushing instead a nostalgic vision of the autocratic regime of Zine el-Abidine Ben Ali that preceded it.

"Saied you are going the wrong way... your plans are catastrophic for the country," said Karima Jouini, 44, a teacher attending the march in central Tunis that was led by Moussi.

The most vocal opposition to Saied has come from the moderate Islamist Ennahda party, the largest in the suspended parliament and a key player in successive governments since the revolution.

Moussi and her Free Constitutional party are bitterly opposed to Ennahda, casting it as the cause of Tunisia's main problems over the past decade and she has not criticised any of Saied's moves targeting Islamists.

However, while Saied has focused almost entirely on reconstructing the political system and purging his opponents, he has done very little to address Tunisia's economic problems.

"Rest assured, we will not let them dismantle the state and continue with individual rule," Moussi said, addressing the protest.

"If we remain silent, we will become a country whose food is sent to it in planes, like the poorest countries in the world," she added.

The country faces a crisis in public finances for which it has embarked on talks for a rescue package with the International Monetary Fund, but Tunisians already face shortages of staple goods including flour, semolina and sugar.

"Saied kidnapped the country just to impose his own project, but he has led it to famine," said another protester who gave his name as Imed.