* Nine killed in election day violence, underlining disorder
* Vice-President Abd-Rabbu Mansour Hadi is sole candidate
* Seeks mandate for new constitution, holding free elections
* Voting ends early after attacks on Aden poll centres (Adds official's quotes on voting cut short in south)
By Joseph Logan and Mohammed Mukhashaf
SANAA/ADEN, Feb 21 (Reuters) - A general took power in Yemen on Tuesday as the sole candidate in a presidential election after a year-long uprising that ousted long-serving ruler Ali Abdullah Saleh but left the poor Arab country still teetering on the brink of chaos.
The election confirms Abd-Rabbu Mansour Hadi, who served as Saleh's vice president and close confidant, as president. He is tasked with implementing a power-sharing deal with Saleh's political opponents under an agreement negotiated to remove Saleh after 33 years in power.
Yemen's uprising was one of the bloodiest of the revolts that have swept across North Africa and the Middle East. Saleh becomes the fourth Arab autocrat toppled in the wave of unrest that began in Tunisia more than a year ago. His sons and nephews retain command of powerful military units and security agencies.
In a reminder of the daunting task his successor faces holding Yemen together, at least nine people were killed in election-related violence that cut voting short in southern Yemen, where separatists demanded an election boycott.
"Elections are the only exit route from the crisis which has buffeted Yemen for the past year," Hadi said after voting.
Minibuses plastered with posters of Hadi and decked out with speakers sped around the capital Sanaa blaring out pop songs to shouts of "Vote to Save Yemen."
Saleh, now in the United States for treatment of burns suffered in an assassination attempt last June, joins Tunisia's Zine al-Abidine Ben Ali, Egypt's Hosni Mubarak and Libya's Muammar Gaddafi as leaders toppled in the "Arab Spring".
He leaves behind an economy in shambles, a rebellion in the north, separatism in the south, a tenacious wing of al Qaeda, and a divided military still partly dominated by his kin.
Long queues formed early in the morning outside polling stations in Sanaa amid tight security, after an explosion ripped through a voting centre in the southern port city of Aden on the eve of the vote.
"We are now declaring the end of the Ali Abdullah Saleh era and will build a new Yemen," prominent Yemeni human rights activist Tawakul Karman, who shared this year's Nobel Peace Prize, said as she waited to cast her ballot outside a Sanaa university faculty.
Voters dipped their thumbs in ink and stamped their finger prints on a ballot paper bearing a picture of Hadi and a map of Yemen in the colours of the rainbow.
Yellow taxis careened through Sanaa with young men sticking their arms out of the windows waving their freshly dyed thumbs.
TURNOUT SEEN CRUCIAL, HIT BY VIOLENCE
A high turnout would lend Hadi the legitimacy he needs to carry out changes outlined in the U.S.-backed power transfer deal brokered by Yemen's Gulf neighbours, including the drafting of a new constitution, restructuring the armed forces and preparing for multi-party elections in two years' time.
Turnout, which one official estimated was as high as 80 percent, was hit by violence in Aden, where an election organiser said attacks forced voting to end by mid-afternoon.
"There was a boycott, and when those who were boycotting found they weren't winning they turned to resistance and seized ballot boxes and stormed polling places," Mohammed Hussein al-Hakimi told reporters in Sanaa. He said final election results could take as long as 10 days to emerge.
Election committee official Khamis al-Dayani earlier said nine of some 300 large polling districts were unable to begin voting for security reasons, and that an election official had been killed in the southern city of Taiz.
Southerners, who accuse the north of grabbing their resources and discriminating against them, are demanding a divorce from the north. The two regions were separate countries until they were united in 1990, and fought a civil war in 1994.
Security forces fired on protesters throwing stones during an anti-election rally in front of a polling station in al-Hota, the capital of the southern Lahej province, killing two, witnesses and local officials said.
An officer from the Republican Guards and an armed secessionist were also killed during clashes in the port city of al-Makalla, capital of Hadramout governorate, officials said.
The streets of Aden were nearly deserted and intermittent gunfire could be heard. Masked youths carrying rifles and machine guns patrolled junctions, preventing people from reaching polling stations.
Gunmen attacked voting centres in the districts of Khor Maksar, Mansoura and Maala in the Aden vicinity at dawn, killing one soldier, residents said. They stole ballot boxes and set them on fire in the street.
A leader in the Southern Movement, Abdulhamid Shokri, said four civilians including a child had died in Aden since the morning as a result of clashes between security forces and people opposed to the election.
PARTNERS IN CRIME
The northwest of the country is largely controlled by an insurgent group known as Houthis, whom Saleh tried to crush before a ceasefire in 2010. They have expanded their territory as central government authority crumbled, and called for a boycott of the vote.
"These are not real elections, it is just formalising the American-backed GCC initiative which aimed to control the Yemeni revolution," said Dayfallah al-Shami of the Houthis' leadership council, referring to the Gulf Cooperation Council regional group of states. "It is just a reproduction of the same regime."
The vote was supported by the United States and Yemen's rich neighbours led by Saudi Arabia, who - alarmed at signs of al Qaeda exploiting political upheaval to strengthen its regional foothold - threw their weight behind the power transfer deal.
But the poll was denounced in advance by some of the youth activists who first took to the streets to demand Saleh's ouster. They regard the transfer plan as a pact among an elite they see as partners to the crimes of Saleh's tenure, including the killings of protesters in the uprising against him.
Some demonstrators dyed their thumbs red in protest at the elections and in memory of those killed during the uprising.
The interim government faces a fiscal and humanitarian crisis, and has sought billions of dollars in international aid since unrest has all but paralysed modest oil exports that fund imports of food staples.
Washington - which has said it wants a united Yemeni leadership as a partner in its campaign against al Qaeda - is likely to play a role in an impending donors' conference. Yemen is one of the countries that allow U.S. forces to use drone aircraft to strike al Qaeda militants.
The United Nations Children's Fund says 57 percent of Yemen's 12 million children are chronically malnourished - the highest level outside Afghanistan - and half a million face death or disfigurement from poor nutrition.
The U.N. envoy who helped seal the transition pact denounced the violence in the south as a violation of the Security Council resolution that echoes the deal's terms. He also called for donor cash to avert the collapse of the country.
"They need to step up to the mark and start supporting Yemen if they want to see it survive the transition. The government is still financially crippled," said Jamal Benomar.
"Expectations are high and if people do not see some improvement in their daily lives, then further unrest is a serious possibility." (Additional reporting by Tom Finn and Mohammed Ghobari in Sanaa, Isabel Coles in Dubai; Writing by Joseph Logan and Sami Aboudi; Editing by Peter Graff)