The national elections in the Philippines for 2016 have begun, with over 100,000 police officers tasked to tighten up security amid fears of election-related violence.

Five candidates are in the running to succeed President Benigno Aquino III as president of the nation. Voters are also set to choose the new vice-president, 12 senators and about 18,000 congressional and local officials, according to Fox News.

Ahead of the polls, 71-year-old Davao mayor Rodrigo Duterte remained the frontrunner in the voter-preference surveys.

Other presidential candidates – Liberal Party (ruling party) standard-bearer Mar Roxas, senators Grace Poe and Miriam Defensor-Santiago and Philippine vice-president Jejomar Binay – following closely behind.

Elections in the Philippines have long been marred with numerous controversies. Violence, the murdering of cheating accusations, vote buying and candidates criticizing one another have often dominated the news.

Aquino, whose term ends in June, encouraged Filipinos to show to the world that the country can maintain elections that are peaceful and organized despite various political differences.

A total of 15 people have been killed during the election period, with the latest victim being a mayoral candidate from the south who was murdered on Saturday.

Police also reported that independent local candidate Armando Ceballos was killed when a gunman stormed his house and shot him dead, according to BBC News.

Killings are not the only issue that has plagued the country during the election campaigns, as the government had also to deal with a 23-year-old information (IT) graduate who committed a security breach.

The breach gave out 228,605 e-mail addresses, 1.3 million passport numbers and expiry dates of overseas Filipino voters, as well as 15.8 million fingerprint records.

Before the candidates filed their certificates of candidacy back in October, over 130 people had applied for candidacy for the presidential position, which included one who claimed that he had the support from aliens coming from outer space.