The centre-left Social Democrats, led by Milos Zeman, secured 32.1 per cent, but were far short of winning a parliamentary majority, with only a handful of results still to come.
The centre-right Civic Democratic Party of former prime minister Vaclav Klaus was second with 27.7 percent of the vote, according to the poll.
The poll confirmed earlier indications that the Social Democrats, led by Milos Zeman, could have a chance to form a centre-left coalition government for the first time since the anti-Communist revolution in 1989.
Despite the Social Democrat lead, Jacques Rupnik, a Czech-born political analyst, said voting patterns have not changed drastically since the last parliamentary election in 1996.
That election ended with Klaus, who won clearly in 1992, falling just short of a majority, and forming a quarrelsome three-party centre-right coalition that lacked the unity and parliamentary strength to undertake major reform. It fell apart last winter over a party financing scandal.
The elections have been held two years early. A caretaker government under banker Josef Tosovsky has been running the country since Klaus was ousted last December.
Despite the expected victory, the Social Democrats lack a clear majority and will have to go through painful negotiations to form a government coalition.
Mr Zeman's potential partners are the small Christian Democrats, who came fourth with 9 per cent of the vote and the Freedom Union - a new party favoured by President Vaclav Havel - who received 8.7 per cent. The populist single-issue party, Pensioners for Secure Living, failed to clear the 5 per cent threshold needed to get any seats in the 200-member lower house of parliament. -APReuse content