LA PAZ — Bolivians voted on Sunday in a presidential election that opinion polls suggested would force a December runoff, threatening to end nearly two decades of dominance by the Movement for Socialism party. Electoral authorities reported steady turnout across the Andean nation.

The vote came against a backdrop of the worst economic crisis in a generation, marked by fuel shortages, dwindling dollar reserves and inflation that has eroded household purchasing power. The Supreme Electoral Tribunal oversaw polling stations from La Paz to Santa Cruz, deploying observers from the Organization of American States and the European Union.

The left arrived deeply fractured, with President Luis Arce and former leader Evo Morales split by a bitter feud that hollowed out the once-hegemonic MAS. Opposition figures, including centrist and business-friendly candidates, campaigned on promises to restore fiscal stability and attract foreign investment to the gas-dependent economy.

Pollster Ipsos Ciesmori had forecast that no candidate would reach the 40 percent threshold, or a 10-point lead, needed to avoid a second round. A runoff would set up a decisive contest over the country's economic direction and its ties with regional powers.

The Supreme Electoral Tribunal said preliminary results would be released after polls closed, with a final count to follow in the days ahead. International observers pledged to publish assessments of the vote's conduct.