KANO, Nigeria, April 18 (Reuters) - Rioting erupted across Nigeria's largely Muslim north on Monday and the Red Cross said many people were killed as youths torched churches and homes in anger at President Goodluck Jonathan's election victory.
The vote count showed Jonathan, from the southern oil-producing Niger Delta, had beaten Muhammadu Buhari, a former military ruler from the north, in the first round.
Observers have called the poll the fairest in decades in Africa's most populous nation but Buhari's supporters accuse the ruling party of rigging and his Congress for Progressive Change Party rejected results announced so far.
Those results show how politically polarised the country is, with Buhari sweeping the north and Jonathan winning the largely Christian south.
The Nigerian Red Cross said churches, mosques and homes had been burned in rioting across the north.
"A lot of people have been killed but early reports are still coming in," Red Cross official Umar Mairiga told Reuters.
Authorities in the northern state of Kaduna imposed a 24-hour curfew after protesters set fire to the residence of Vice President Namadi Sambo in the town of Zaria and forced their way into the central prison, releasing inmates.
The body of a small boy shot in the chest by a stray bullet was brought to a police station, a witness said.
"They have destroyed our cars and our houses. I had to run for my life and I am now in my neighbour's house," said Dora Ogbebor, a resident of Zaria whose origins are in the south.
Plumes of smoke rose into the air in parts of the state capital as protesters set fire to barricades of tyres. Security forces fired in the air and used teargas to disperse groups of youths shouting "We want Buhari, we want Buhari".
Police said the violence was being orchestrated by those who refused to accept the election results rather than being motivated by religion or ethnicity.
Buhari was yet to make any public statement on the disturbances.
The former general's spokesman said he believed the vote count had been manipulated against him.
"We cannot accept these results as announced until cross-checks have been carried out by the electoral commission," Yinka Odumakin told Reuters.
Soldiers used whips to disperse people in the streets of Kano, the most populous city in the north. Protesters hurled stones in the backstreets. Several churches were burned and authorities imposed a curfew.
Nigeria has a history of rigged and violent elections but Saturday's vote was deemed by many Nigerians, and foreign observers, to have been a vast improvement on the past, with the voting process orderly and little unrest on the day itself.
"Election day showed a generally peaceful and orderly process," said chief European Union election observer Alojz Peterle. EU observers said 2007 elections were not credible.
A Reuters tally of results put Jonathan on nearly 23 million votes to just over 12 million for Buhari.
The Independent National Electoral Commission was expected to announce all the results on Monday and to formally declare Jonathan the winner.
The outright win for Jonathan could ease worries over potential disruptions to crude exports from Africa's biggest oil and gas industry -- far away from the disturbances in the north.
It could also lift local financial markets which had been unnerved by the prospect of a potential run-off and the All-Share Index <.NGSEINDEX> was up nearly 3 percent in early trade to its highest in nearly a month.
But Buhari's camp -- which had urged its supporters throughout the campaign to make sure their votes counted -- said some results looked suspicious, especially where turnout had been exceptionally high in some of Jonathan's strongholds.
Buhari, who also lost elections in 2003 and 2007, has repeatedly said Nigerians would not accept another rigged vote. He told Reuters on Saturday he would not go to court to challenge the outcome but that his party may chose to do so.
(Additional reporting by Mike Oboh in Kano, Sahabi Yahaya and Joe Bavier in Kaduna, Austin Ekeinde in Port Harcourt; Writing by Nick Tattersall; Editing by Matthew Tostevin)