The ex-Soviet Central Asian nation of 5.3 million people on the border with China faces a key test, for in its 20 years of independence the deeply divided nation has not had a peaceful transition of presidential power. Polling stations opened at 08:00 am (0200 GMT) and will close at 7:00 pm (1300 GMT), with provisional results expected overnight Sunday to Monday. Voters have 16 presidential candidates to chose from and will cast their vote at one of the 2,289 polling stations throughout the mountainous country. Almazbek Atambayev, the country's moderate prime minister, is thought to be the frontrunner. He faces challenges from two Kyrgyz nationalists: Kachimbek Tashiyev of the Ata Zhurt party; and the former speaker of parliament, Adakhan Madumarov. Tashiyev, a former boxer, draws his support from the divided south, where almost 500 people died last June in ethnic clashes between Kyrgyz and ethnic Uzbeks that forced hundreds of thousands to flee their homes. He and Madumarov have both warned of mass protests if the elections are judged to be fraudulent. Madumarov told AFP earlier this week that in the case of fraud he would organise protest rallies. Tashiyev told reporters on Friday that "millions" would rise up if the elections were seen to be unfair. Interim President Roza Otunbayeva, the former diplomat who led the uprising that toppled the Kyrgyz nationalist Kurmanbek Bakiyev from power in April 2010, is not allowed to stand in Sunday's race. But she is a close ally of Atambayev. Two days ahead of the poll, Otunbayeva warned candidates against inciting "illegal acts that destroy stability." The April 2010 uprising was the second revolution of Kyrgyzstan's independence after the 2005 Tulip Revolution that ousted post Soviet leader Askar Akayev and installed Bakiyev in his place. Kyrgyzstan, the only country in the world that hosts both US and Russian military bases, is an important partner for US operations against the Taliban.