Former soccer star George Weah's camp said on Wednesday he was set to win Liberia's presidential election run-off against Vice President Joseph Boakai in the country's first democratic transfer of power in more than seven decades.

Weah's deputy campaign manager for operations, Morluba Morlu, said his prediction was based on precinct-level vote tallies he said were trickling in from across the country after Tuesday's vote.

Liberian election officials began counting the votes from Liberia's 15 counties on Wednesday and planned to announce preliminary results in the afternoon, with final results due on Thursday.

But unofficial partial results announced on local radio stations all showed the favourite Weah in the lead, and Morlu said he expected his candidate to win with about 70 percent of the vote.

"It is clear. We are only waiting for the (election commission) to announce the results and declare him president," Morlu said. "We are calling on ... Boakai to concede defeat and congratulate George Weah."

Officials from Boakai's ruling Unity Party were not immediately available for comment but his supporters at party headquarters were circumspect about Boakai's prospects.

"We are listening to the result that the radio is giving. At least we are satisfied with Lofa County results," said Jerry Mulbah, referring to Boakai's home county in northern Liberia, where unofficial results showed him in the lead.

Liberia, Africa's oldest modern republic, was founded by freed U.S. slaves in 1847, but its last democratic transfer of power occurred in 1944.

Weah and Boakai are vying to succeed outgoing President Ellen Johnson Sirleaf, whose 12-year rule cemented peace in the West African country after civil war ended in 2003.

Many Liberians have criticised Johnson Sirleaf for not doing enough to root out endemic poverty and corruption and are eager for fresh leadership.

Weah, who was named world footballer of the year in 1995, was runner-up to Johnson Sirleaf in the 2005 election and has positioned himself an outsider who will deliver tangible benefits to the country's young population.

Turnout on Tuesday appeared much lower than the first round in October but people in the capital Monrovia expressed relief that the vote had gone smoothly, after several candidates said the first round was marred by fraud.

The Supreme Court ultimately dismissed a legal challenge brought by the third-place finisher and backed by Boakai but the proceedings delayed the second round by more than a month.

"It's free and fair and transparent," said Kamhdiggs Kemah, 48, of Tuesday's vote. "We saw the whole process, so I am very happy with it. And I know my next leader will be George Weah."