Afghan men line up for the registration process before they cast their votes Saturday at a polling station in Kabul, Afghanistan. Afghans flocked to polling stations nationwide, defying a threat of violence by the Taliban to cast ballots in what promises to be the nation's first democratic transfer of power.

KABUL, Afghanistan — Afghans flocked to polling stations nationwide Saturday, defying a threat of violence by the Taliban to cast ballots in what promises to be the nation’s first democratic transfer of power. The turnout was so high that some polling centers ran out of ballots.

The excitement over choosing a new leader for the first time appeared to overwhelm the fear of bloodshed in many areas, as Afghans embarked on a major transition nearly 13 years after the U.S.-led invasion toppled the rule of the Taliban.

President Hamid Karzai, the only leader the country has known since the Islamic movement was ousted, is on his way out, constitutionally barred from a third term. International combat troops are leaving by the end of the year. And Afghans are left largely to on their own to face what is likely to be an intensified campaign by the Taliban to regain power, even as authorities face higher public demands to tackle entrenched poverty and corruption.

Men in traditional tunics and loose trousers and women clad in all-encompassing burqas waited in segregated lines at polls under tight security. At a Kandahar hospital-turned-polling station, the men’s line stretched from the building, through the courtyard and out into the street. In Helmand province, women pushed, shoved and argued as they pressed forward in a long line.

The vote is the first for Afghans in which the outcome is uncertain. Voters are choosing from a field of eight presidential candidates, as well as selecting provincial council members. With three front-runners in the presidential race, a runoff was widely expected because none is likely to get the majority needed for an outright victory.