"The closing time for voting has been pushed to midnight in all provinces due to high turnout," the official SANA news agency quoted Syria's Higher Judicial Committee for Election as saying, according to Xinhua.
Syria's general election started at 7:00 a.m. Tuesday amid criticism from Western countries and threats from the armed opposition. It was previously scheduled to end at 7:00 p.m.
In a previous statement, the committee said that turnout in Tuesday's voting was "beyond expectations", adding that some 220 more ballot boxes were distributed in the afternoon due to the large number of voters.
More than 15 million eligible and registered voters are expected to cast their ballots for the country's three presidential contenders, including incumbent President Bashar al-Assad.
The interior ministry said 9,610 polling stations are available across the country, amid reports that the government has also set up ballot boxes in displacement shelters to allow thousands of displaced Syrians to participate in the voting process.
The vote is taking place despite rejection from the opposition and its Western backers, who have dismissed the poll as a "farce."