Tunisian police blocked hundreds of demonstrators from reaching electoral commission offices on Thursday as protesters took to the streets against a referendum on a new constitution that would expand the president's executive powers.

President Kais Saied proposed the new constitution this month that would limit the role of parliament and boost his own rule. The constitution will be put to a referendum on July 25 in a vote most political parties have already rejected.

Saied has ruled by decree since last summer, when he dissolved the parliament and the democratic 2014 constitution, moving towards one-man rule and vowing to remake the political system. Critics have described the move as a coup.

The protesters, led by Free Constitutional Party leader Abir Moussi, chanted "people, revolt against the dictator's rule" and "shut down fraudulent electoral body."

Police forced back protesters who had attempted to break through barriers in front of the electoral authority's headquarters in Tunis, leading to minor clashes.

Amid a large security presence, the protesters shouted "No retreat, no fear."

Local polls say Moussi's Constitutional Free Party would win by a large margin over rivals in any parliamentary elections.

Moussi is a supporter of Zine El Abdine Ben Ali, who was toppled in a 2011 revolution in the country.

With less than three weeks before the vote, the referendum does not set a minimum requirement for voter participation, meaning the changes could come into effect with a relatively small voter turnout.