* Jonathan takes strong lead, Buhari does well in north
* Observers see better vote than in the past
* Opposition voices concern, unrest in north (Adds result declarations adjourned until Monday, barricades)
ABUJA, April 17 (Reuters) - President Goodluck Jonathan secured election victory on Sunday as votes were tallied from around Nigeria, fuelling anger in the mainly-Muslim strongholds of rival Muhammadu Buhari.
Buhari, a former military ruler from the arid, dustblown north, had hoped to at least force a second round against Jonathan, the first head of state from the swamps and creeks of the oil-producing Niger Delta.
But a Reuters tally of results from 35 of 36 states across Africa's most populous nation showed Jonathan on 22 million votes to 12 million for Buhari. Nowhere near enough voters were registered in the remaining state for him to catch up.
Observers called the election the fairest for decades.
But Buhari's camp said some results looked suspicious, especially where turnout had been exceptionally high. In a sign of the growing tension in the north, youths set up burning barricades in several cities.
Jonathan's officials said there would be no victory claim until results were announced by the Independent National Electoral Commission. They were clearly upbeat.
"This is no time for triumphalism. It is a time for deep reflection, for strengthening the bond of our union and for all of us to work together," Oronto Douglas, a senior advisor to Jonathan, told Reuters.
With formal announcements of results still awaited from eight states, the electoral body adjourned until Monday, the earliest the winner is likely to be declared. <^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Reuters Insider preview: link.reuters.com/rah98r Graphic on elections: link.reuters.com/xet78r For more stories, background and analysis: [nLDE68H051] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
The president did particularly well in his predominantly Christian south, while Buhari swept many northern states in the country of 150 million people.
An outright win for Jonathan could ease worries over potential disruptions to crude exports from Africa's biggest oil producer and lift local financial markets awaiting the end of a series of elections.
But the voting made clear the challenge of ethnic and religious polarisation facing the election winner alongside the need for reforms to Africa's third-biggest economy, held back by poor infrastructure, mismanagement and corruption.
"While a near term relief rally is easily plausible in Nigerian financial markets, the political impetus behind real reform, and the extent to which theses challenges are met head-on, will be the determinant of longer term outcomes," Razia Khan, Standard Chartered's Africa economist, told Reuters.
Heading African Union observers, former Ghanaian President John Kufuor said Nigeria appeared to have ended its reputation for badly flawed elections and could set an example for Africa with at least a dozen more African polls due this year.
"I expect the developments here will have a very positive impact on the continent," he told Reuters.
The prospect of victory for the candidate of the ruling People's Democratic Party (PDP) grated in the north, which had been buoyed by early results showing Buhari doing very well and had feared rigging.
There was unrest in parts of Adamawa, Bauchi, Gombe, Kaduna and Maiduguri. Youths took to the streets and set up burning barricades. A Reuters correspondent in Kaduna saw several plumes of smoke over the city.
"There are protests all over. People are waiting to see how Buhari will react," said one security source.
Buhari's supporters questioned results including those showing turnout as high as 86 percent of registered voters in Niger Delta states and the southeast.
"In most of the southeast and south-south, no real elections took place," said former government minister Nasir el-Rufai, a Buhari supporter. "In the southwest and the north, the results have no relation to what happened at the polling units and we will prove it in due course," he told Reuters.
Buhari's spokesman Yinka Odumakin said irregularities had been seen, but any challenge would come after the vote count.
Buhari's support was bolstered by a feeling among many in the north that Jonathan is usurping their right to another four years in power. Jonathan inherited office after his predecessor, northerner Umaru Yar'Adua, died last year in his first term, interrupting a rotation between north and south.
Some northern voters were resigned and said that at least their votes had been counted this time.
"If it is the people's will, God's will then people must welcome Jonathan without a heavy heart because it was a fair fight," said Mohammed Ibrahim, 33, the driver of a three-wheeler rickshaw taxi in the ancient Islamic city of Kano.
(Additional reporting by Joe Brock in Kano, Joe Penney and Segun Owen in Yenagoa; Editing by Nick Tattersall)
(For full Reuters Africa coverage and to have your say on the top issues, visit: af.reuters.com/ )