Zimbabwe police vowed to crack down on any attempts to leak early results from Tuesday's vote, complicating plans by some civic groups to pre-empt official announcements by the country's election commission.
The move means it could be hours before the first officially collated results trickle in from the Zimbabwe Electoral Commission, although political parties will have immediate access to individual results posted at polling stations.
President Robert Mugabe is fighting to extend his 33-year rule in the election pitting him against main rival Morgan Tsvangirai, prime minister for the last four years under an enforced unity government brokered after a contested 2008 vote was marred by violence.
Police thwarted plans to collate election results posted outside polling stations by declaring it an offence to send results via text messaging or the Internet, said Frances Lovemore, a senior official at the Zimbabwe Election Support Network.
"At a lot of the polling stations, they've locked the public out. They're clamping down now," she told Reuters.
The Mail and Guardian newspaper, published by a Zimbabwean in neighbouring South Africa, earlier set up a Website it said would compile preliminary results based on electoral commission break-downs.
"Preliminary results are not meant to announce or declare that any particular candidate or political party is the winner," it said on the site.
Police warned at a news conference that they would act against "people who announce results of elections before the Zimbabwe Electoral Commission", news networks reported.
Police spokeswoman Charity Charamba could not be immediately reached for comment.
Zimbabweans are eager to hear the outcome of the vote, which was peaceful on the whole - unlike recent previous polls - and which they hope will unlock crucial Western donor aid needed to spur growth. Aid has been suspended over policy differences with Mugabe.
No reliable opinion polls have been released, making it difficult to gauge whether Tsvangirai will manage to defeat Mugabe.
The 89-year-old Mugabe, who denies rigging past votes to hold onto the power, says he is confident of victory, but has pledged to concede defeat should it happen.
Tsvangirai has also predicted an overwhelming win. Both Mugabe's ZANU-PF party and the Movement for Democratic Change, led by his opponent, could reject results of the poll, which was dogged by logistical hitches ahead of the election.
About 6.4 million people, or half the population, were registered to vote. Results are expected within a five-day deadline intended to prevent a repeat of problems seen in the last election in 2008, when big delays triggered violent clashes.
(Additional reporting by Ed Cropley; Editing by Stacey Joyce)