Prime Minister Almazbek Atambayev has won Kyrgyz presidential election after sweeping more than 60 percent of the votes, the Central Asian state's central election commission says. 

With 99 percent of ballots counted, pro-business Prime Minister Almazbek Atambayev had 63 percent of the vote, an outright majority that would avoid the need for a second round run-off against a potentially strong rival from the south, Reuters reported on Monday.

The vote is a test of reforms designed to make Kyrgyzstan, a landlocked country of 5.5 million, Central Asia's first parliamentary democracy after 20 years of authoritarian rule that triggered a bloody revolution in April last year.

A trouble-free election would signal the first peaceful transfer of power in the mainly Muslim country, which lies on a drugs route out of nearby Afghanistan and hosts both Russian and U.S. military air bases.

It was the first presidential election in Kyrgyzstan since the uprising of 2010 that toppled former President Kurmanbek Bakiyev. 

In his election campaign, Atambayev said he would shut down a U.S. military base outside the capital Bishkek and bring stability to the nation. 

He also promised to bring prosperity and stability to the former Soviet republic during his campaign. The former Soviet republic has a population of 5.3 million people.

But international observers reported cases of ballot box stuffing and vote buying, while a group of candidates vowed to challenge the result even before the polls had closed on Sunday.

Atambayev's two main challengers from a field of 16 each polled just below 15 percent. Both enjoy strong support from Kyrgyz nationalists in the poorer south of the country, scene of ethnic riots that killed hundreds in June 2010.

About 200 supporters of third-placed Kamchibek Tashiyev, a trained boxer popular in the south, rallied in the southern city of Jalalabad and blocked a major road. Dozens more of his supporters gathered in Osh, the largest city in the south.

Both Tashiyev and Adakhan Madumarov, a three-times national billiards champion who was placed second, have said their actions would be lawful, but have refused to rule out street protests.

Tashiyev demanded new elections. "I won't calm down," he told reporters in the capital Bishkek. "Voters are in place and you will hear their reaction soon."

Per capita GDP in Kyrgyzstan, at below $1,000, is less than a tenth of that in its oil-rich neighbor Kazakhstan. The economy relies heavily on remittances from migrant workers and the production of a single gold mine.

Atambayev, born in the Russian-leaning north of Kyrgyzstan, is the flag-bearer of reforms set in motion by outgoing leader Roza Otunbayeva, the former ambassador to London and Washington who became caretaker president after the revolution.

The reforms have watered down the powers of the president and established parliament as the main decision-making body, changes opposed by the prime minister's main challengers.

"Kyrgyzstan doesn't need an authoritarian system. We should decide every issue together," a relaxed Atambayev told reporters. "The strength of any president, of any politician, lies in having the trust of the people."

In comments sure to please Moscow, he said he did not support the presence of the military base at Manas airport near Bishkek, which is used by the U.S. military to support the war in Afghanistan. The lease expires in 2014.

The Organization for Security and Cooperation in Europe's election observer mission said it was "cautiously optimistic" about the future of democracy in Kyrgyzstan, but noted flaws with the compilation of voter lists and tabulation.

"It's disappointing that the problems on election day did not live up to the democratic promise," Corien Jonker, head of the mission of the OSCE's Office for Democratic Institutions and Human Rights, told a news conference.

"Our observers reported a number of cases of ballot-box stuffing, multiple and family voting, vote buying and the transport of voters from polling station to polling station with the intention of multiple voting," she said.

The OSCE also noted positive aspects to the election: its pluralism, competitiveness and respect for fundamental freedom.

Atambayev is a popular choice among residents of Bishkek and other regions of the country's north. He said both his main challengers were "good politicians" and that "every strong person" was capable of working the good of the country.

"Atambayev has shown he can work for his people and for the republic," said Turat Sheikinov, 56, chairman of an agricultural workers' co-operative. "There is a person here that can attract foreign investment."

But disenchantment was evident among ethnic Kyrgyz voters in Osh. "My personal opinion is that the results could not be further from the truth," said a university professor who gave his name only as Kamil.

Within the south, voting was split roughly along ethnic lines. While Tashiyev and Madumarov polled well among the Kyrgyz population, many ethnic Uzbeks voted for Atambayev.

They said Atambayev's close ties with Russia were their best hope of protection from a repeat of ethnic violence.

"All sane citizens want Atambayev. They don't want an ethnic feud," said Begin Tavokyalov, 48, who makes a living selling melons in an ethnic Uzbek neighborhood of Osh.

The next president will be allowed by the current constitution to serve a single six-year term and will appoint the defense minister and national security head. He will need to work hard to weed out corruption and revive an ailing economy.

"We are living from loan to loan. The law doesn't work," said Bishkek housewife Gulsaira Tezekbayeva, 45, who was recently laid off from her job as a laboratory technician. "I personally fear for our people. Life isn't sweet."