Lima quit the PAICV after losing the nomination on a platform of bolstering human rights earlier this year. But he retains support of some key party officials and is considered the favourite against Sousa, who has promised to draw investment into the impoverished islands.

Analysts say the split within the PAICV could benefit the election's opposition candidate, Jorge Carlos Fonseca from the MPD party, who is seen as a potential challenger to Lima in a second round that would be held on August 21 if needed.
The PAICV and the MPD have dominated politics since independence from Portugal in 1975, each running Cape Verde for a 10-year stint since multi-party democracy was introduced in 1991.

The country has a parliamentary system in which the president has reduced powers, and the government -- currently dominated by the PAICV -- decides most policy.

The fourth candidate, Joaquim Monteiro, is also running as an independent but is not expected to escape the first round, according to opinion polls.

If no candidate wins a majority in the first round, a run-off between the two top finishers will be held.

Cape Verde's lack of resources and chronic drought have led to mass emigration of much of the population, which numbers a little over 500,000. But the government has developed the tourism industry and is seeking to turn the islands into a trade and transport hub.