LAGOS : Nigerians were on Saturday voting to choose new state governors and local assemblies, with the main opposition party tipped to build on its victory in the presidential race.

Some 760 candidates are in the running for 29 governor and deputy governor positions, while 5,290 hopefuls are seeking local assembly seats in all 36 of Nigeria's states. The main opposition All Progressives Congress (APC) is expected to benefit from Muhammadu Buhari's presidential win against incumbent Goodluck Jonathan, of the Peoples Democratic Party (PDP). The PDP currently has 21 governors while the APC has 14. "The still-ruling PDP will likely lose its majority of the governorships, partly from the bandwagon effect, incumbency fatigue and the APC's momentum in regions like the southwest and Middle Belt," the Eurasia Group said in a briefing note on Friday.

But the group's head for Sub-Saharan Africa, Philippe de Pontet, said the key state of Rivers, in the oil-producing southern delta region, would go to the PDP.

Governors are increasingly influential figures in Nigeria's federal system of government, exercising near-total control over their states, including finances and projects at the local level. As a group they have become a considerable force to counter or bolster presidential power.

Polling stations opened from 8 am (0700 GMT), with mixed reports of election officials having arrived early and swift accreditation to the non-arrival of volunteers and materials.

In Rivers - a key prize for both sides because of the huge revenues from the oil and gas sector largely based in the state - APC supporters alleged rigging on the part of the PDP in one area.

Animosity between outgoing APC governor Rotimi Amaechi and Jonathan plus previous fraud claims at the presidential vote have provided for high tension and fears of violence.

Police spokesman Ahmad Muhammad said part of the local electoral commission office was burnt down in Buguma, the hometown of former Niger Delta militant Mujahid Dokubo-Asari.

There were also sporadic incidents of shots fired, police said, while officers and soldiers were out in force in the state capital, Port Harcourt. But voter Bright Owabie, a businessman, told AFP: "I expect the election to be fair and free: no violence. Let the people's vote count."

Elsewhere, a close race is predicted between APC candidate Akinwunmi Ambode and the PDP's Jimi Agbaje for control of Lagos, which drives Nigeria's economy.

The megacity of 20 million people and the surrounding state of the same name have been in opposition control since Nigeria returned to civilian rule in 1999.

APC spokesman Lai Mohammed claimed in a statement that "thugs armed by the PDP" were "on (the) rampage, shooting sporadically to scare away voters and carting away voting materials".

There was no immediate confirmation of the claim or a response from the PDP.

The APC could oust the PDP in the central state of Plateau and in the northern state of Kaduna, where nearly 70 percent of people voted for Buhari, experts predict.

Buhari and his wife, Aisha, accredited without a hitch in his home town of Daura, in neighbouring Katsina state. Jonathan was registered at his home in Utuoke, in southern Bayelsa.

Nigeria could also see its first female governor, with the APC's Aisha Jummai Alhassan running in Taraba state.

Voting was again taking place inside camps for people made homeless by the Boko Haram insurgency in the Borno state capital, Maiduguri.

Nationwide, Nigeria's police and security services have ordered restrictions on the movement of vehicles during polling hours and closed the country's land borders.

Fears of poll-related violence and attacks by Boko Haram Islamists provided the backdrop for the presidential elections but despite several sporadic incidents, widespread violence did not materialise.

But the government has called for a similar level of vigilance.

Handheld devices to authenticate voter identities are again being used in order to cut electoral fraud that has blighted previous elections, despite some malfunctions two weeks ago.

Problems with some of the machines in recognising biometric details stored on voter ID cards, including those of Jonathan, forced the election to go into a second day in some places.

Results of the gubernatorial and state assembly votes are expected to come in from Sunday, with winners announced in individual states.

Jonathan, 57, remains president until May 29 when Buhari, 72, is inaugurated as head of state.