Nigerians voted for state governors Tuesday in the last of three landmark ballots, amid deep concern over security after the presidential vote ignited an explosion of deadly unrest.

The vote comes after 16 April presidential elections led to widespread rioting across the mainly Muslim north of Africa's most populous nation, leaving more than 500 dead, according to a local rights group.

Unrest broke out despite what some observers said appeared to be Nigeria's cleanest vote for head of state since a return to civilian rule in 1999, with the country seeking to break from a history of deeply flawed polls.

The election won by President Goodluck Jonathan exposed deep divisions in Nigeria, particularly between the country's economically marginalised north and predominately Christian south, home to the oil industry.

Voters in the main northern city of Kano, one of the areas hit hard by the rioting, lined up at polling places Tuesday morning, but turnout so far appeared far below that of the presidential election.

"I am out here again to exercise my civic right, hoping that this time around I will get what I vote for," said Shamsu Adamu, a 26-year-old student. "I have no fear of violence because, in most cases, violence erupts after elections when people allege rigging."

Most of Nigeria's 36 states were holding governorship and state assembly polls. Security was tight, with curfews and military patrols having largely brought calm to the continent's largest oil producer.

The ruling Peoples Democratic Party was projected to lose a number of states and many races were expected to be closely fought, raising concerns that desperate politicians may seek to rig the vote.

Some analysts believe that could set off another round of violence, with much of the initial rioting following the presidential election believed to have started over allegations of rigging.

Nigeria's state governors wield significant power and preside over large budgets thanks to revenue generated by the country's oil industry. They play influential roles in national politics, and the seats are highly sought after.

The ruling party currently controls some 27 state governorships, but it faces tough challenges.

In the southwest, the Action Congress of Nigeria opposition, which is in power in the economic capital Lagos, will be looking to gain more ground.

The Congress for Progressive Change, the party of ex-military ruler Muhammadu Buhari, Jonathan's main challenger in the presidential vote, appears set to make gains in the north.

Nigeria's enormous effort to hold credible polls after a series of badly flawed ballots is seen as giving a greater opening for opposition parties.

But there were fears that turnout would be reduced due to last week's violence, which the Red Cross estimates displaced some 74,000 people. Initial indications from a handful of polling stations showed low turnout, but no conclusions could yet be drawn.

Jonathan, a southern Christian, defeated Buhari, a Muslim from the north, by a score of 57 per cent to 31 per cent in the presidential vote.

There were allegations of rigging in the north, including from Buhari himself, though observers hailed the election as a major step forward for Nigeria.

A completely new voter list was compiled with the use of electronic fingerprinting and various safeguards were put in place in an effort to prevent election-day rigging and ballot-box snatching.

Observers note that serious problems remain, but say the parliamentary elections on 9 April -- which had to be postponed from 2 April -- and the presidential vote constituted significant improvements.

Not all states will be voting Tuesday. Kaduna and Bauchi states will hold their state elections on Thursday due to deadly unrest there.

A total of 26 states, including Kaduna and Bauchi, will hold governorship ballots this week, while all 36 will hold state assembly polls.

The other 10 states will not hold governorship ballots at this time because of court cases over previous election results that delayed the start of governors' terms of office.