As millions of Filipinos headed to the polls to vote in national elections, three security guards were killed and a fourth was wounded when gunmen opened fire at a polling station in the southern Philippines, according to AFP.

Elections in the Philippines are traditionally a dangerous time in the Philippines, with gun laws and violent political culture, making election season particularly turbulent.

The shooting took place in Buluan Municipality after polling stations opened on Mindanao Island, where multiple armed groups are active. In another incident in Datu Unsay Municipality late Sunday, nine people were left wounded when five grenades exploded outside a polling station.

Just minutes after the Datu Unsay attack, a grenade exploded in a neighboring municipality but left no casualties. 

Police said victims of the grenade attacks had walked from remote mountain villages to cast their vote, some walking eight to 12 hours to reach the polling station.

58 people were massacred in 2009 in Maguindanao in what is known as the deadliest incident of political violence in the country when gunmen working for a local warlord attacked a group of people to prevent a rival from filing his candidacy papers. Dozens of the victims were journalists covering the event.

There had been 16 election-related incidents in the Philippines since January 9, including four shootings, as of Sunday.