Nigerians on Saturday voted for a second time in a fortnight in governorship and state assembly elections, with heightened concerns from observers of violence and an increased military presence.
Elections for governors are being held in 29 of Nigeria's 36 states, for all state assemblies, plus the administrative councils in the Federal Capital Territory of Abuja.
Polling stations opened at 0700 GMT, with results expected from early next week.
Late on Friday the Situation Room umbrella of more than 70 civil society monitoring groups expressed concern of an "escalation of violence between and within political parties and their supporters."
There were concerns in several states of the "partisanship of security agencies" and "an intimidating presence of military personnel," the group said, reporting that military fighter jets and helicopters had been deployed in parts of the country.
Two people were killed and 35 vehicles destroyed in violence between political supporters in the southwest state of Lagos on Friday, the Situation Room said.
The electoral commission said a fire destroyed voting materials at one of its offices in Akwa Ibom state, in the south.
President Muhammadu Buhari will be expecting to consolidate his victory on February 23, when he won 19 states to secure a second, four-year term of office.
His All Progressives Congress (APC) currently controls 22 states while the main opposition Peoples Democratic Party (PDP) has 13.
The All Progressives Grand Alliance (APGA) has one.
Governors are powerful and influential figures in Nigeria's federal politics, controlling state finances, where they are responsible for key areas including education to health.
They can also provide a strong collective voice in Abuja.
State-level elections are often predicted to broadly mirror presidential polling and this year come amid concerns about the role of security forces during the vote.
During the presidential and parliamentary polling, there were reports of violence, vote-buying, voter intimidation and ballot box vandalism in some states.
At least 53 people were killed, according to the Situation Room, which said safety fears contributed to a low turnout.
- Rivers -
The Situation Room said last month's poll did not meet the minimum standard for a credible election, although most domestic and international observers disagreed.
Delays in voting and disruption in parts of the country saw the PDP and its beaten candidate Atiku Abubakar brand the results a "sham" and take legal action.
The party has especially questioned the use of troops, which are not responsible for election security, citing reports soldiers had blocked voters from polling units.
Tensions have been running high since the electoral commission postponed the scheduled vote for a week just hours before it was due to begin on February 16.
That prompted the two main parties to accuse each other of conspiring to rig the result.
Buhari revealed he had also ordered soldiers to be "ruthless" with vote riggers and anyone attempting to disturb voting would be risking their life.
Nigeria has a history of electoral violence, particularly volatile Rivers, in the heart of the oil-producing southern delta.
The PDP governor, Nyesom Wike, accused the military of complicity in the killing of 16 people in the Abonnema area of the state.
Adding to tensions this time is a court ruling barring any APC candidates from standing in the gubernatorial election because of procedural irregularities in the selection process.
An AFP reporter in the Rivers state capital, Port Harcourt, said there was a heavy military presence on the streets.
Lagos to Kano
Other states being keenly watched include Lagos, in the southwest, where APC candidate Babajide Sanwo-Olu is facing a strong challenge from the PDP's Jimmy Agbaje.
Control of the commercial capital is a key prize given its sheer size and role as the main driver of the country's economy.
Kano, in the northwest, sees the APC governor, Abdullahi Umar Ganduje, seeking a second term, despite being caught on camera apparently accepting large amounts of cash in bribes.
The scandal earned him the nickname "Gandollar" but is not seen as affecting his chances unduly, given a fractured opposition.
But supporters have clashed with those of his influential former boss Rabiu Kwankwaso, who is supporting his son-in-law Abba Kabiru Yusuf as PDP candidate.
Voting in the religiously mixed northwestern state of Kaduna is likely to be along ethnic and religious lines, as APC governor Nasir El-Rufai is running on an all-Muslim ticket.
Central Plateau, Taraba and Benue states, hit by renewed violence between farmers and nomadic herders, will also be watched given dissatisfaction at Buhari's response.