Polls opened on Sunday in Cameroon as Africa's oldest leader is widely expected to win another term even as separatists threaten to disrupt the election and many who have fled the unrest are unable to vote.President Paul Biya has held office since 1982 and vows to end a crisis that has killed more than 400 people in the central African nation's Southwest and Northwest territories in the past year. The fractured opposition has been unable to rally behind a strong challenger to the 85-year-old leader.A victory likely would come with a weakened mandate for Biya as many residents of the troubled English-speaking Southwest and Northwest regions have fled elsewhere. By law, voters can only cast a ballot in the community where they are registered.More than 200 000 people have been displaced because of violence by both separatists and the military in those regions, with many towns simply abandoned.More than 6.6 million people across Cameroon are registered to vote. The Election Commission and government say they will make provisions for displaced voters, but many say they will not be able to vote amid threats by separatists. Cameroon also battles with Boko Haram extremists in its Far North, where more than 230 000 people have been displaced.Cameroon's government has said that anyone who tries to organise chaos on election day "risks being disagreeably surprised."The ruling Cameroon Peoples Democratic Movement has attempted to campaign as normal in the affected regions, holding several rallies, but Biya has never appeared. The party says at least eight of its officials have been abducted and some supporters attacked.Election observers, including the African Union, have said they will not be carrying out their work in the troubled southwest and northwest because of the crisis.What began as protests two years ago by teachers and lawyers in the English-speaking regions against what they called the marginalisation by majority French speakers turned deadly after a government crackdown. The separatists emerged, cheered on by some in Cameroon's diaspora, including the United States.Then fringe groups became violent, clashing with security forces that have been a close ally of the US in regional counterterror efforts but face accusations of human rights abuses. Panicked civilians are caught in the middle.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.