Provisional results from Sunday's first round poll on Anjouan in the Comoros Islands indicate three candidates who will contest May's presidential race.
The next president must come from the island of Anjouan
In terms of a power-sharing deal among the three islands, it is Anjouan's turn to name candidates for the final round.
Observers see the poll as a key test of whether the archipelago can make the transition to peaceful politics.
Since independence from France in 1975, the country has witnessed 20 coup attempts - four of them successful.
The candidates reportedly chosen by Anjouan voters are:
- Ibrahim Halidi, allied to the outgoing federal administration
- Ahmed Abdallah Sambi, a religious leader
- Mohamed Djaanfari, a former officer in the French air force.
At some polling stations voting was delayed as materials arrived late, and in compensation was extended by an hour in the evening at the affected stations.
Under the constitution and political agreements reached in 2001, the union presidency rotates every four years between the three semi-autonomous islands that make up the Comoros: Grande Comore, Anjouan and Moheli.
The elections are being seen as a test of how successful this power-sharing arrangement has been.
The 13 candidates in the Anjouan primaries included veteran politicians, former military officers and prominent Islamists.
The line-up of candidates this year included women for the first time.
The three candidates who gain the highest vote tallies from Anjouan will go on to stand in national elections on 14 May, in which voters from among the population of all 670,000 Comorans will vote.
The union president has two deputies who must not come from the same island as the president.
The elections are being carefully scrutinised by South Africa, as well as by the African Union (AU) and Arab League.
South Africa is leading a 460-strong AU mission which began operations in the capital, Moroni, on 30 March.