The commission in charge of Russian elections, which are considered neither free nor fair, said its online voting system had malfunctioned on Friday due to the large number of people trying to cast their vote that way.
On the first of three days of voting, some 500,000 people in Moscow alone cast their votes online in the morning, the central election commission said.
Moscow's leadership would like to see the highest possible voter turnout in order to label the vote as legitimate.
Officials said turnout had reached 24% and that 27 million people had voted by Friday evening.
In places, the vote was organized in part like a festival with folk performances and singers.
It is all but certain that Russian President Vladimir Putin, 71, will emerge victorious for the fifth time. Russian state pollsters predict Putin, who has been in power for almost a quarter of a century, will get more than 80% of the vote. That would be the highest result ever for him.
The head of the A Just Russia party, Sergei Mironov, who openly supports Putin, dropped his completed ballot paper into the transparent ballot box - without an envelope.
Putin has three rivals, which lends the election a veneer of credibility. But they not only have no chance, they also hold Kremlin-friendly political views and usually show support for Putin.
Candidates who spoke out against Putin's war in Ukraine were not allowed to run.
Election observers from the Organization for Security and Co-operation in Europe (OSCE) have not been invited to monitor the polls.
The election supervisor and close Putin confidante, Ella Pamfilova, said more than 333,000 people are observing the election and everything was proceeding "normally."
At the same time, however, she had to admit that there were irregularities in online voting right from the start. Officially, she attributed the problems to a large number of voters who wanted to cast their votes online.
In contrast, the independent election monitoring organization Golos, which is politically persecuted in Russia, said that no genuine election observers were deployed.
Golos spoke of large-scale election fraud, noting that in many places, state officials and employees of large, partly state-owned corporations are being pressured to vote.
"The first day of voting has begun and everything is going exactly as we warned: from the morning onwards there was pressure on a huge number of voters," Golos co-chair Stanislav Andreychuk wrote on Telegram.
There were some acts of civil disobedience. According to authorities, men and women poured paint into ballot boxes in several polling places across the country to invalidate the ballot papers inside.
Arson attacks were reported from St Petersburg and Moscow, as were several arrests.
The deputy head of the electoral commission in Moscow, Nikolai Bulayev, claimed that the protests were "externally controlled" and called for greater monitoring of polling stations.
However, the largest protest action is not planned until Sunday.
Kremlin opponents are calling on Russians to show up outside polling stations at exactly noon and use the ensuing long lines to express their dissatisfaction. They have called on voters to invalidate ballot papers by writing in more than one check per ballot.
Moscow puts the number of eligible voters in Russia at 114 million - but this figure actually includes 4.5 million people in the occupied parts of the Ukrainian regions of Donetsk, Luhansk, Zaporizhzhya and Kherson. Ukraine called the vote illegal.
UN Secretary General António Guterres criticized Russia for allowing voting in Ukrainian territory.
"The secretary general condemns the efforts of the Russian Federation to hold its presidential elections in areas of Ukraine occupied by the Russian Federation," his spokesman Stéphane Dujarric said in New York on Friday.
"He recalls that the attempted illegal annexation of regions of Ukraine has no validity under international law."
Voting in the massive country with its 11 time zones will continue until Sunday evening, when the last polling stations close in Kaliningrad on the Baltic Sea at 8 pm (1800 GMT).
