With nearly a million votes counted in Sierra Leone's presidential election, opposition challenger Ernest Koroma remains in the lead, according to the National Electoral Commission (NEC).

In provisional results posted at 3 pm, Sierra Leone time, on Wednesday, the NEC said results were in from half the country's polling stations.

Koroma had 564,927 votes so far, or 59 percent of the total counted. Vice-President Solomon Berewa of the ruling Sierra Leone People's Party (SLPP) had 41 percent, or 400,218 votes.

It is expected that it will take some days before final results emerge. In the first round of elections, Koroma's All People's Congress (APC) won Parliament, but he failed to draw enough votes to win in the first round of presidential balloting.

The NEC reported a high turnout at the polls - it said 72 percent of voters had cast ballots at the polling stations which had reported.