Voters in Uzbekistan are casting ballots Sunday in the tightly controlled, ex-Soviet nation's first presidential election since the death of Islam Karimov, the authoritarian leader who ruled for 27 years.

Acting President Shavkat Mirziyoyev, who spent 13 years as Karimov's prime minister, is expected to easily win a five-year term in the Central Asia country.

Karimov led Uzbekistan since before the Soviet collapse, first as its communist boss and then as president.

During his long tenure, he ruthlessly crushed all opposition, silenced the media and was repeatedly denounced by international human rights groups for abuses that included killings and torture.

Karimov also never cultivated a successor. His September death raised concerns that the predominantly Sunni Muslim nation of 32 million might see fierce infighting over its leadership that could allow radical Islamists to rise to power or exploit the situation. But the 59-year old Mirziyoyev shifted into the acting president's job quickly and without any visible tensions, highlighting apparent consensus between regional clans.

In Sunday's election, Mirziyoyev faces three nominal rivals. Two of them, Hotamjon Ketmonov and Narimon Umarov challenged Karimov in past elections, each receiving about 3 per cent of the vote.

However, neither candidate has campaigned as a vocal critic of Mirziyoyev, while the fourth contender, Sarvar Otamuratov, has been just as pliant.

The Organisation for Security and Cooperation in Europe, the main trans-Atlantic security and rights group, deployed an observer team to monitor the election. It has described the campaign as “strictly regulated” and “moderately visible.”

“There is no perceptible exchange of views among the candidates with regard to their programs,” the OSCE said in an interim report.

“All candidates refrain from criticising the government or each other, and claim to target distinct segments of the electorate.”

Under Karimov, Uzbekistan's relations with its ex-Soviet neighbors were strained by disputes over water, energy and other issues. Analyst Arkady Dubnov noted in a commentary for the Carnegie Moscow Center that Mirziyoyev has worked quickly to ease tensions.

Dubnov also pointed to Mirziyoyev's pledge to liberalise foreign currency trading as a sign that he was planning to ease some of the rigid rules established under Karimov.

Since gaining independence in 1991, Uzbekistan has pursued a policy of economic self-reliance and sought to balance its diplomatic ties with the West and Russia, playing them against each other.

Uzbekistan, Central Asia's most populous nation, is rich in natural resources and borders Afghanistan, making it of strategic interest to Russia, the United States and China.

Shortly after Karimov died, Russian President Vladimir Putin visited Uzbekistan and met with Mirziyoyev, a trip that reflected Moscow's desire to strengthen its influence in the country.

The United States installed a military base in the country for action in Afghanistan after the Sept 11, 2001, terrorist attacks. Washington was forced to abandon the facility in 2005 as relations between the Uzbekistan and the US soured following a government crackdown on rioters in the Ferghana Valley city of Andijan that is believed to have left hundreds dead.

Almost all Western media long were barred from reporting inside Uzbekistan, and the country's independent journalists and activists have faced sustained harassment.