* Opposition leads in provisional results - local media
* Exit poll shows 63% of votes for opposition - officials
* Voters queue from Saturday night; police raid opposition office
* Observers denounce repressive campaign, lack of transparency
* International monitors stay away, fearing vote-rigging
Opposition candidate Ibrahim Mohamed Solih has taken a 15 percentage point lead over incumbent Abdulla Yameen in the Maldives' presidential election, according to early provisional counts reported by local media.
Yameen was expected to cement his grip on power, amid criticism over the fairness of the vote on the islands, best known as a luxury holiday destination.
Voting closed at 1900 hours, after the Indian Ocean nation's Election Commission extended voting by three hours due to long queues at polling stations.
The provisional results counted in 250 out of 472 vote boxes as of 1640 GMT, showed the opposition leading by a margin of 15.4%, according to local media, Mihaaru. The provisional results for the remaining 222 vote boxes, with an estimated 130,000 voters are yet to be released.
The opposition said their own exit polls showed their candidate had secured 63% of vote, and added that they were closely monitoring the count.
Yameen's party officials told Reuters that results from areas where he has strong support have still to be released.
The Muslim-majority Indian Ocean nation has become a theatre of rivalry between its traditional partner, India, and China, which has backed Yameen's infrastructure drive, and prompted concern in the West about Beijing's increasing influence.
Yameen's government has jailed many of his main rivals, including former president and his half-brother, Maumoon Abdul Gayoom, on charges ranging from terrorism to corruption.
More than a quarter of a million people were eligible to vote across the coral islands. Yameen, 59, is seeking a second five-year term.
Hundreds of people queued outside polling stations in the capital, Male, early on Sunday. On some islands, people started queuing on Saturday night.
"I am voting to revert a mistake I made in 2013. I am voting to free President Maumoon (Gayoom)," Nazima Hassan, 44, told Reuters after voting in Male.
Abdul Rasheed Husain, 46, in Male said he cast his ballot for Yameen to take the Maldives "to the next level".
In the polling booth at the Maldives embassy in Colombo, some voters had to wait for more than seven hours.
Ahamed Ihusan, a 24-year-old business management student, told Reuters that "if it is a free and fair election, the opposition will win."
Many opposition supporters blamed the Election Commission for the delays.
"Yameen is trying to frustrate voters by having a shoddy process for the elections and a long waiting time of 6-8 hours in some stations. I appeal to all to be patient and not step back," an opposition supporter told Reuters, asking not to be named.
Mohamed Shareef Hussain, Maldives envoy to Colombo, said the Electoral Commission had not assigned enough staff, causing delays.
Police late on Saturday raided the main opposition campaign office saying they came to "stop illegal activities", after arresting at least five opposition supporters for "influencing voters", opposition officials said.
British Ambassador James Dauris wrote on Twitter that it was "easy to understand why so many people are concerned about what might happen on Election Day".
Monitors stay away
Most poll monitors, including those from the European Union and the United Nations, declined the government's invitation to observe the election, fearing their presence might be used to endorse Yameen's re-election even after possible vote rigging.
Rohana Hettiarachchi, a member of the Asian Network for Free Elections (ANFREL), which was named as an election monitor, said his organisation could in fact not take part.
"Our four members were invited and the Elections Commission published our name in the international monitors list. But we did not get the required visa," he told Reuters.
Transparency Maldives, one of the few election monitors on the ground, said the initial vote had gone smoothly.
The opposition's joint candidate, Ibrahim Mohamed Solih, known as Ibu, told supporters he was confident of victory.
"I appeal to everyone not to allow any space for unrest tomorrow," he told a rally on Saturday. "Let the voting end peacefully and let the people decide what they want. The people are hungry for a change."
Yameen also urged voters to head to the polls and said he was confident of the work he had done in his first term in office to put the nation on a path of development.
The country has been in political turmoil since February, when Yameen imposed a state of emergency to annul a Supreme Court ruling that quashed the convictions of nine opposition leaders, including Mohamed Nasheed, the country's first democratically-elected leader and former president.
Yameen has disregarded calls from the United Nations, several Western countries and India for an amicable solution to the crisis.
Ahead of the vote, Human Rights Watch urged foreign governments to press the Maldives to uphold democratic rights.
"Should the Maldives government fail to do so, they should impose targeted sanctions, such as those proposed by the European Union, against senior ruling party officials implicated in abuses," the New York-based group said in a statement.