Nicaraguan President and ex-guerrilla leader Daniel Ortega was set for a strong win to a third term, with 66 percent of six percent of votes counted in elections marred by irregularities.

Right-wing radio host Fabio Gadea won 26 percent of votes counted so far, said the head of the electoral council some five hours after polling closed, as Ortega's Sandinista supporters already celebrated.

"We win," shouted thousands of jubliant supporters of Ortega's former Marxist rebel Sandinista National Liberation Front in the capital Managua and other major cities, before the announcement of official results.

Ortega, 65, has presided over economic growth in Central America's poorest nation with generous aid from his leftist ally, Venezuelan President Hugo Chavez, and by savvy deals with former foes in the church and business elite.

He also faced a fractured opposition in a vote marred by accusations of irregularities and complaints from international observers of "difficulties" to monitor the polling.

Tension has risen since a November 2009 Supreme Court ruling cleared the way for Ortega to seek a third term as president. Consecutive re-elections and third terms were supposedly banned.

In pre-election surveys, Ortega had 48 percent support -- 18 points higher than his closest rival, 79-year-old conservative Gadea.

To avoid a run-off, Ortega would need more than 40 percent of the vote, or at least 35 percent and a lead of more than five percentage points.