Nigeria's ruling party consolidated its power with two wins in weekend state governorship elections that were marred by violence and vote-rigging claims.

State elections are fiercely contested in Nigeria, where governors are powerful figures and clashes, killings and voter intimidation are common.

Despite a heavy security presence, there were several reports of deadly shootings, and an election official was abducted ahead of the vote.

Saturday's polls were held in three states.

President Bola Ahmed Tinubu's ruling All Progressives Congress (APC) won a landslide victory in southeastern Imo state, where the current governor Hope Uzodinma secured a second term with 540,308 votes, according to official election tallies.

The Peoples Democratic Party (PDP) candidate came second with 71,503 votes.

The APC also retained power in central Kogi state, where Ahmed Usman Ododo was declared winner with 446,237 votes. The Social Democratic Party (SDP) candidate came second with 259,052.

The incumbent PDP governor was leading in southern Bayelsa state, but the final results have been delayed.

The Centre for Democracy and Development (CDD), which observed the elections, said there was low turnout at several polling stations, with people "scared of coming out to vote due to fear of violence".

Monitoring groups and Nigerian media reported several deadly shootings, including one in which military officials allegedly killed a man trying to run off with a ballot box in Anyigba, Kogi state.

The army and police have not responded to requests for comment.

The CDD also described widespread vote-buying, with some people exchanging their ballots for handouts of rice.

Observers were watching the electoral commission closely after the presidential vote earlier this year, when critics and the opposition said delays uploading results and technical problems created opportunities for rigging ballots.

The Independent National Electoral Commission (INEC) said it had "done everything possible to guarantee that the weekend's election was free, fair, and credible."

INEC said an official "abducted while waiting to board a boat" in Bayelsa ahead of the vote had since been released.

Another boat carrying election documents capsized, it said, affecting more than 5,000 voters in the state.

Nigeria has a long history of electoral violence since the country emerged from military rule in 1999 and many vote results end up challenged in the courts.