Preliminary results show that the turnout for the referendum on a new constitution in Tunisia is around 27.54 percent, head of the Independent High Authority for Elections (ISIE) said on Monday evening.

More than 2,458,985 voters participated in the vote, but the number "remains an estimation" as the results of some polling stations have not yet reached the polling center, said ISIE President Farouk Bouasker.

Tunisia started the referendum in its 24 provinces on the country's Republic Day, which fell on Monday.

Polling stations across the country opened doors to a total of 9,278,541 registered voters at 6 a.m. local time (0500 GMT).

The final results of the referendum will not be announced until the deadlines for appeals have passed, but no later than August 28.