BISSAU, Guinea-Bissau (AP) — Guinea-Bissau is holding a presidential election against a backdrop of political tension and unrest on the streets of the impoverished West African country.

Twelve candidates are running for head of state, including the incumbent, Jose Mario Vaz, who has been in power since 2014.

If no candidate captures more than 50% of Sunday’s vote, a runoff ballot is to be held between the two top candidates on Dec. 29.

Guinea-Bissau, a former Portuguese colony of around 1.5 million people, is one of the world’s poorest countries. It has been plagued by political instability, poverty, corruption and drug-trafficking. The most recent military coup was in 2012.

Last month, one person died and three were injured when police used tear gas to break up an unauthorized street march organized by opposition parties.