Uzbekistan on Sunday declared its presidential ballot valid after more than the required third of voters turned out in an election that 77-year-old strongman incumbent President Islam Karimov is almost certain to win.

The central electoral commission of the ex-Soviet Central Asian country said 36.55 percent of the 20 million registered voters had cast their votes in the first four hours, passing the threshold of a third stipulated by Uzbek law for an election to be valid.

Voting at more than 9,000 polling stations across the country began at 6.00 am local time (0100 GMT) and was set to continue until 8.00 pm (1500 GMT).

Karimov, who has ruled the country since before the collapse of the Soviet Union, is standing against three candidates put forward by parties in the Uzbek parliament that openly support his presidency.

While exit polls are prohibited, many voters in the capital Tashkent told AFP they had voted for the incumbent.

Burkhon, a 63-year municipal transport mechanic who declined to give his surname, cited periodic unrest in neighboring Kyrgyzstan and Tajikistan, as well as the ongoing crisis in Ukraine, as reasons for casting his vote for Karimov.