The presidential candidate of Sierra Leone's ruling party holds a slim lead over the opposition leader based on certified tallies seen by Reuters from nine of the 16 voting districts, though many opposition strongholds have not yet reported.

Samura Kamara of the All People's Congress (APC) secured 50.80 percent of the nearly 1.94-million votes certified so far from Saturday's election - a lead of about 30 000 votes over Julius Maada Bio of the Sierra Leone People's Party (SLPP), the tallies showed.

In the remaining seven districts, Bio claimed over 100 000 more votes than Kamara in last month's first round, in which the two finished neck-and-neck.

Kamara, a former foreign affairs minister, and Bio, who briefly ruled the West African nation as head of a military junta in 1996, are vying to replace outgoing President Ernest Bai Koroma, who cannot seek re-election due to term limits.

The largely peaceful election process has come as a relief for the country of 7-million people, who endured a civil war in the 1990s and whose economy was dragged down by an Ebola epidemic in 2014-15 and a global slump in commodity prices in 2015.

But tensions have risen since the election with each side saying it is on track to win. Bio alleged that his Freetown home was targeted by gunfire from a security guard deployed to a neighbour's house after polls closed on Saturday. The neighbour, a government minister, denied any shots were fired.