Opponents of President Alexander Lukashenko have called for a mass rally after polls is due to close at 2000 (1800GMT), to protest against electoral fraud.
Mr Lukashenko has warned he will crush any attempt to stage a popular revolt.
His administration has been widely criticised in the West for its authoritarian rule.
Prior to the vote, scores of opposition supporters were detained and a number of foreign election monitors barred.
Chief opposition candidate Alexander Milinkevich predicted that fraud would return President Lukashenko to office with 70 percent of the vote.
Police have said that protesters "trying to destabilise the situation" will be treated as terrorists and could face the death penalty.
A spokesman for the human rights organisation, the Helsinki Committee, said the Belarussian government's threats to opposition groups could trigger violence.
BBC
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