Both President Yameen Abdul Gayoom and the opposition candidate, Ibrahim Mohamed Solih, voted in the capital, Male, shortly after polls opened.
More than 260,000 of the 400,000 Maldivians were eligible to vote at about 400 polling stations across the islands that comprise the Indian Ocean archipelago.
Observers from Transparency Maldives said in a statement late Sunday morning that opening procedures "went well," with nearly all of the polling stations opening within 30 minutes of the scheduled opening time.
Hundreds waited in line as a light rain fell in Maldives' capital, Male.
Voters debated the relative merits of the two candidates in front of a polling station at the Imauddin School.
Aviation worker Mohamed Ismail, 23, said he cast his ballot for Solih because "people live in fear" under strongman President Yameen, who has been criticized for cracking down on democratic freedoms.
"Look around. People are moving freely," countered Adam Thaufeeg, a 40-year-old government employee, who said he voted for Yameen because of his vision for developing the Maldives.
An election-eve police raid of Solih's main campaign office cast a pall over Sunday's elections.
A police warrant obtained by The Associated Press cited police intelligence that Solih's campaign office may have been used to coordinate vote-buying. Senior campaign official Ahmed Shahid was named in the warrant as a suspect. Repeated calls to Shahid went unanswered.
The raid Saturday was the latest sign of a government crackdown against the opposition, raising fears that the election may be rigged to favor Gayoom's party.
Gayoom used his first term in office to consolidate power, jailing opponents, including his half brother, a former president, and two Supreme Court Justices, and asserting control over the courts.
The European Union said Friday that it was not sending election observers because the Maldives had failed to meet the basic conditions for monitoring.
"In view of events in Maldives," the country's British ambassador, James Dauris, tweeted Saturday, "it's easy to understand why so many people are concerned about what might happen on Election Day."
The polls close at 4 p.m. and results are expected after 10 p.m., election officials have said.