(Updates with Lagos result in paragraph 3)

By Camillus Eboh

ABUJA, April 15 (Reuters) - Opposition supporters burned buildings, blocked roads and barricaded election offices in Nigeria on Sunday as early results from flawed state elections showed a big victory for the ruling party.

Nigerian newspapers estimated about 50 people were killed in violence linked to rigging in Saturday's vote for 36 state governors, which should give Nigerians an idea of what to expect at the presidential poll on April 21.

The ruling People's Democratic Party (PDP) held on to 11 of 14 states where results were announced by the electoral body. Opposition parties won three, including the largest city, Lagos, which was already an opposition stronghold.

"They have awarded themselves almost every state. It's incredible," said Lai Mohammed, a spokesman for the opposition Action Congress.

In the southern oil-producing state of Delta, where the PDP was announced the winner, youths armed with cutlasses and guns burned houses and blocked roads in the city of Warri while hundreds of women and children fled on the back of motorcycles.

"They are blocking everyone to show their anger. They are burning buildings and I heard sporadic gunfire," said a taxi driver in Warri who gave his name as Famous.

Community leaders said there was no voting across much of the riverine state, where the campaign stoked ethnic discord.

A series of militant attacks on oil facilities in Delta last year forced thousands of foreign workers to flee and cut the OPEC member nation's output by a fifth.

Democracy returned to Africa's most populous nation in 1999 after three decades of almost continuous army rule, and these elections should lead to the first civilian-to-civilian transition since independence in 1960.

President Olusegun Obasanjo must step down next month after serving two four-year terms.

VULNERABLE

The PDP won 28 of 36 states in the last polls in 2003, and there are about eight states where its dominance was threatened.

Saturday's polls were disrupted by late or non-arrival of ballots, theft of ballot boxes, kidnapping of election officers, voter intimidation, fake results sheets, mistakes in the voter register, faulty ballots and under-age voters, witnesses said.

"If people impose themselves on the electorate it's no better than military rule. The erosion of our democracy is horrendous," Senate President Ken Nnamani said from his native Enugu state, where he said there was almost no voting.

Opposition groups in several states said rigging was so widespread as to merit a fresh election. Youths barricaded INEC offices in two states, Ondo and Bauchi, where PDP state governments faced strong opposition. There were street protests in southwestern Osun state, where PDP was announced the winner.

Police chief Sunday Ehindero said protests would not be tolerated.

INEC said it was generally satisfied, but it cancelled the poll in southeastern Imo state due to irregularities and said it would be rerun on April 28. The PDP fielded no candidate in Imo.

Dozens of people have been killed in political violence in the months leading up to the poll. Diplomats said the credibility of the exercise was already in doubt because dozens of mostly opposition candidates were disqualified by controversial indictments for fraud. (Additional reporting by Estelle Shirbon in Okurieke, Daniel Flynn and Tume Ahemba in Lagos, Tom Ashby in Abuja, Ardo Hazzad in Bauchi and Austin Ekeinde in Port Harcourt)

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