Tunisia has approved a new constitution granting unchecked powers to the office of President Kais Saied, the electoral board said, after a poorly attended referendum in which voters overwhelmingly backed the document.

Saied's rivals accused the electoral board controlled by Saied of "fraud" and said his referendum held on Monday had failed.

On Tuesday evening, electoral commission head Farouk Bouasker told journalists the body "announces the acceptance of the new draft constitution for the Republic of Tunisia," based on preliminary results, with 94.6 percent of valid ballots voting "yes" on 30.5 percent turnout.

Monday's vote came a year to the day after the president sacked the government and suspended parliament.

"Tunisia has entered a new phase," Saied told celebrating supporters after polling closed. "What the Tunisian people did... is a lesson to the world, and a lesson to history on a scale that the lessons of history are measured on," he said.