AFP - Populist opposition leader Michael Sata was sworn in Friday as Zambia's new president, after a campaign vowing to clean up corruption and to help the poor enjoy the country's recent economic growth.

"I will discharge my duties as president diligently, and I take my responsibility without fear or favour," Sata said in reciting his oath at the Supreme Court, broadcast live on national television.

The election was marred by sporadic violence that left two people dead on Thursday, but the streets in Lusaka were joyous as Sata's supporters scaled walls and climbed trees in hopes of glimpsing the ceremony.

Scores of police on horseback or in riot helmets stood by, but outgoing President Rupiah Banda quickly conceded defeat, diminishing the chance of more unrest.

"Speaking for myself and my party, we will accept the results. We are a democratic party and we know no other way," Banda said in his farewell speech at State House.

Sata's swearing-in makes Zambia one of the few African countries to have the ruling party change democratically twice since independence.

Observers said the violence had not compromised the elections, and found no evidence of fraud in the voting.

Sata won with 43 percent of the vote against Banda's 36 percent, a victory that analysts said was fuelled by the nation's poor majority who have yet to experience the economic boom, boosted by heavy Chinese investment in mining.

"His win was very much driven by people in the informal sector, people who felt they were left out of the economic boom," said Lee Habasonda from the Southern Africa Centre for the Constructive Reconciliation in Lusaka.

"Stricter controls on how foreign investors do business in the country are expected," he said.

Banda's Movement for Multi-party Democracy (MMD) has ruled since Frederick Chiluba unseated independence leader Kenneth Kaunda in the first democratic elections in 1991.

But Chiluba's graft trial changed perceptions of the party once seen as a champion of democracy.

Convicted of corruption in a London court, Chiluba was acquitted in Lusaka. Banda's government refused to appeal, and he disbanded the anti-corruption team that had brought the case to trial.

In his farewell speech, Banda conceded his party may have made mistakes.

"Zambia was liberated by an MMD ideal but maybe we became complacent with our ideals. Maybe we did not listen, maybe we did not hear," he said.

Banda was also perceived as cosy with foreign investors, after repealing a 25 percent windfall tax on miners.

Sata has promised to strengthen Zambia's anti-corruption investigators and to review the tax code -- likely to result in higher mining taxes that he says will help the nearly two thirds of Zambians living on less than two dollars a day.

"There's no harm in slightly more aggressive Zambian policies," said Matthew McDonald of the Centre for Chinese Studies at South Africa.

Since 2007, China has poured an estimated $6.1 billion into Zambia, where the gross domestic product last year stood at about $17 billion.

Five years ago, during an earlier presidential bid, Sata had vowed to chase the Chinese out of the country.

He doesn't make that claim any more, but now will be in a position to win more concessions from Chinese companies, McDonald said.

"Banda has made all sorts of promises regarding lifting people out of poverty... that just haven't come to pass," he said.

"This is an excellent opportunity for an African country to leverage its position with regards to Chinese investment."

Sata's critics fear that this strong-willed firebrand, who has openly expressed his admiration for Zimbabwe's President Robert Mugabe, could prove to be an authoritarian president.

But his stated policies now fall well within the mainstream, as even the International Monetary Fund in recent years has sanctioned higher mining taxes.

"What the form this will take is not clear, nor whether the outcome will necessarily be a negative one," Citibank said in a market commentary.