The Central Election Commission (CEC) reported a turnout of over 90 percent of the 16 million eligible voters, with a 33-percent turnout required to validate the election.
Karimov, a former Communist Party boss who turns 70 in January, is running against what analysts have described as nominal challengers.
Uzbek state television showed Karimov exiting a Tashkent polling station. The president told journalists, "I believe people know what they are voting for and they know it well -- for tomorrow, for peace in our country, for our country's development and prosperity of the people."
And on camera, most voters voiced their support for the only president the country has ever had to stay on for another term.
Roza Tajieva, a resident of the western Khorezm Province, told RFE/RL, "Our entire family voted for [Islam] Karimov. Our president is very dedicated to our people."
One Tashkent resident who only gave his first name as Sunatullo also said he cast his ballot for Karimov. "We are grateful to him because he is building mosques, all enterprises are working," Sanatullo said. "That's why I voted for him."
The three other candidates who registered with the election commission are regarded as Karimov loyalists and have praised him publicly. State television showed all three casting their ballots but none of them spoke to the press as they left the polling stations.
The legal basis for Karimov's candidacy remains unclear, since the Uzbek Constitution bars a president from serving more than two terms.
Karimov's second term expired at the beginning of 2007, and there was no explanation as to why authorities approved his bid last month.
The president has already extended his term in office twice through referendums, in 1995 and 2002.
In the run-up to today's election, Karimov told foreign diplomats that he wanted "a free society and prosperous life" for the republic of 27 million people.
But Human Rights Watch said on December 21 that none of the conditions exist for free and fair elections.
The New York-based group said Uzbekistan's record of restricting opposition political activity and independent media prevents any semblance of a competitive electoral process.
Human-rights activists inside Uzbekistan told RFE/RL's Uzbek Service that there was clear evidence of voting violations at polling stations. In the eastern city of Ferghana, rights activist Abdusalom Ergashev said, "I witnessed several voters casting ballots for their entire families."
Ergashev added that election officials were coaching voters. "At every ballot box, a man and a woman are sitting and advising the voters on checking the proper box [candidate's name], that is voting for Islam Karimov," Ergashev said.
In the central city of Jizzakh, rights activist Bahtiyor Hamroev said he went to several polling stations and was "appalled seeing that many voters are casting three, four, or even six ballots into the boxes."
Opposition websites like uznews.net and unmetronom.com carried similar reports of one person casting multiple ballots. Uznews.net reported a somber mood at polling stations in Andijon, where Uzbek troops opened fire on demonstrators in May 2005. Witnesses said hundreds were killed; the Uzbek authorities put the figure at 187.
Uzmetronom.com also carried a photograph of a small protest earlier by rights activists in Tashkent against the CEC for allowing Karimov to run for an unconstitutional third term.
The CEC reported late in the day that it had not received any complaints about voting violations.
No Media Allowed
A number of media organizations, including the BBC, have been refused permission into the country to cover the election. Viktoria Novikova, the head of the international department of the Russian Channel One, said her channel also did not receive permission to cover the election.
The Organization for Security and Cooperation in Europe (OSCE) has a small team observing the poll.
The OSCE said it would not conduct systematic and comprehensive observation of election-day proceedings due to the "apparent limited nature of the competition."
Molly Stephenson, the press attache at the U.S. Embassy in Tashkent, said, "We have a number of people out from the embassy, observing the election today. And we're still collecting data right now."
Both the OSCE and the U.S. State Department are expected to release assessments of the Uzbek vote this week.
Western election monitors have never recognized an Uzbek parliamentary or presidential election as free and fair or as meeting international standards.
Preliminary results are expected early December 24. Exit polls are prohibited by law.
(RFE/RL's Uzbek Service contributed to this report)