ABUJA, April 14 (Reuters) - Election irregularities sparked pockets of violence across Nigeria on Saturday in a vote which should lead to the first fully democratic transition of power in Africa's most populous nation.

Saturday's election of state governors and legislators was a test of the strength of the ruling People's Democratic Party (PDP) and should give Nigerians an idea of what to expect from presidential polls in a week's time.

Voting began hours late in most places and ballot papers failed to turn up at all in some locations in the north, southeast and southern oil-producing Niger Delta, sparking violent protests and boycotts by the opposition.

Youths protesting the absence of ballots in the southern Anambra and Delta states torched three offices of the Independent National Electoral Commission (INEC). Four people were killed in nearby Benin and Ondo when armed men stormed polling booths to steal ballot boxes, local media reported.

In southeastern Enugu, voting began in the mid-afternoon when polling stations were already due to close.

"Many of us have not voted and we have no chance of voting," said Senate President Ken Nnamani, a PDP member from Enugu, on local television. "Any person being declared a winner as far as Enugu is concerned has no mandate of anybody. People believe that the result has already being predetermined."

The opposition Action Congress said there was no voting at all in many parts of the Niger Delta. A coalition of opposition parties warned INEC not to announce results in northeastern Gombe state because of deficient voting.

"There are massive irregularities and fraud. Soldiers and police have been used to intimidate voters, cart away ballot boxes and rig in favour of the PDP," said Action Congress spokesman Lai Mohammed.

HISTORIC TRANSITION

Nigeria returned to democracy in 1999 after three decades of almost continuous army rule, and this vote should bring the first handover from one elected president to another since independence from Britain in 1960.

Dozens of people have been killed in political violence in the months leading up to the poll. Dozens of mostly opposition candidates have been disqualified over controversial indictments for fraud.

Poor preparation of the voter register and lack of accreditation for observers have also raised doubts about the credibility of the exercise.

"If Nigeria works well, so might Africa. If the democratic experiment in Nigeria stalls, the rest of Africa suffers and loses hope," said Robert Rotberg of the U.S. Council on Foreign Relations in a special report.

Nigerian governors control big budgets and have enormous powers in their states, making the gubernatorial polls as important to many Nigerians as the April 21 presidential vote.

The PDP now controls 28 of the 36 states, with the rest split between a handful of opposition parties.

With unrivalled funds and powers of incumbency, the PDP should coast to victory, analysts say. But endemic corruption, failure to deliver basic services and deteriorating security have boosted the chances of the opposition in many states. (Additional reporting by Ardo Hazzad and Mike Oboh in Kano, Estelle Shirbon and Austin Ekeinde in Port Harcourt, Tume Ahemba and Daniel Flynn in Lagos, Ibrahim Mshelizza in Maiduguri, Ijeoma Ezekwere in Obiaruku)

BUGUMA, Nigeria, April 14 (Reuters) - Voting didn't happen in many parts of Nigeria's richest oil state on Saturday because of poor organisation, attacks and disputes over allegations of vote-rigging, residents and opposition candidates said.

In Buguma, a town in the wetlands of Rivers State, residents said they refused to vote because the result forms provided by officials were photocopies instead of originals.

"We didn't want to vote with the fake result sheets they brought because the PDP boys will use the original ones to rig the election," said Princewill Opunabo, an opposition supporter, referring to the ruling People's Democratic Party (PDP).

"There was no election here today. If they call a result, everyone in the community will know it is a lie," he added.

Ballot boxes and other voting materials lay unused on the floor in the electoral body's local office.

The Asari-Toru local government area, which has its headquarters in Buguma, was expected to be an easy win for the opposition Action Congress, whose gubernatorial candidate Tonye Princewill is a member of the local royal family.

Princewill accused the PDP of trying to steal the election in the whole of Rivers State and said he had written to the electoral commission to protest and demand a new election.

PDP members and electoral officials denied there had been rigging and blamed delays and confusion on logistical hitches.

In Ikwerre, another local government area, gunmen attacked a minibus carrying ballot papers and stole them. The vote was cancelled in one ward, an electoral official said. Local radios reported a similar incident in Ahoada-East local government area, while in Okrika they said angry youths burnt ballots.

COMPLAINTS

A phone-in programme on private radio station Rhythm FM had people calling in from across the state all day to complain there were no functioning polling stations in their wards.

In the state capital Port Harcourt, voting took place but mostly without booths for people to vote in secret.

At a polling station in Mile 3 area, voters had to put their thumbprints on ballot papers in full view of a noisy crowd of electoral officials, members of political parties and fellow voters standing around the table.

A young man who said he was representing the PDP stood over the voters, pointing at the PDP symbol on the ballot papers. Almost all voters put their thumbprint where he indicated. There were at least five other young men from the PDP standing around.

"These boys are not supposed to be there. They are not supposed to be telling the people who to vote for. They are interfering," said Collins Owhonda, a student waiting to vote.

In the last elections, in 2003, Rivers was among several states where there was evidence of significant vote-rigging. The official number of votes cast exceeded the number of registered voters in the state by 200,000.

Like the rest of the oil-producing Niger Delta, it is plagued by violence rooted in poverty and neglect, political rivalries, turf wars between gangs and a dangerous trade in stolen crude. Incidents multiplied in the run-up to the polls

can you provide url?

Thank you o.