Early voting in Lithuania and abroad started on Monday and will continue through Friday. The period was extended to five days for the first time.
Voter turnout in the two-day advance voting period in the 2014 presidential election stood at 2.97 percent.
Voters who are in hospitals and social care establishments, and those in military service and in prisons, can vote by mail in special post offices on Wednesday through Friday.
Disabled people and those who cannot come to their polling stations due to illness, and those aged 70 and older will be able to vote at home on Friday and Saturday.
On Sunday, election day, polling stations will open at 7 a.m. and will close on 8 p.m.
Nine candidates are running for president: European Commissioner Vytenis Povilas Andriukaitis, philosopher Arvydas Juozaitis, MEP Valentinas Mazuronis, economist Gitanas Nauseda, MP Mindaugas Puidokas, MP Naglis Puteikis, Prime Minister Saulius Skvernelis, MP Ingrida Simonyte and MEP Valdemar Tomasevski.
If none of candidates wins at least 50 percent of the vote, the two leading candidates will face each other in the runoff on May 26.
In the referendum on amending Article 55 of the Constitution, citizens are voting on whether or not to reduce the number of Seimas members to 121, from the current 141.
In the other referendum, they are voting on whether or not to amend Article 12 of the Constitution so that Lithuanian citizens by birth do not lose their Lithuanian citizenship when they acquire the citizenship of another country meeting Lithuania's European and transatlantic integration criteria. The criteria would be laid out in a special constitutional law.