Senegal President Abdoulaye Wade is in a tight race with his main rival Macky Sall, according to early unofficial tallies from the most contentious poll in the West African state's recent history, signalling a run-off between the former allies.

The election follows weeks of violent street protests against the 85-year-old Wade's bid for a third term in office despite a two-term limit, and warnings that Senegal's reputation as an established democracy hangs in the balance.

Figures at our disposal indicate that a second round is inevitable, Sall told Reuters Monday.

Partial unofficial results published by website SUNU2012, which has been aggregating figures from volunteers at individual polling stations, showed Wade with about 24 percent, ahead of Sall's 21 percent, with 10 percent of the ballots counted.

Moustapha Niasse, 72, another former ally of Wade's who is also in the race, said that given the results so far, Wade cannot win in the first round, adding that a coalition against Wade in the second round was a must.

Whatever the personality of the candidate who will face him (Wade) in the second round ... in any case, stopping Wade is an imperative, it is a necessity, this is a must, Niasse said on RFI radio.

Prospects could change rapidly, however, as Wade claims strong support in rural areas of the country where figures may be slower to come in. He has said he is confident of a win in the election's first round of voting.

Amadou Sall, a spokesman for Wade, told Reuters that there were not enough votes in yet to draw conclusions.

A candidate must score an outright majority to win in the first round, otherwise the top two candidates compete in a run-off. No official results have yet been released by Senegal's election commission.

Sunday, scores of voters booed Wade as he cast his ballot at his home precinct in an upscale neighbourhood of the capital Dakar. He was ushered away by aides without giving a statement.

Senegal is the only country in mainland West Africa that has not suffered a coup since independence and previous elections have gone mostly smoothly, a record the former French colony has worn as a badge of democratic distinction.

But the run-up to this election has been tense.

Wade's rivals have argued he should not have been allowed to stand due to term limits, but the incumbent has countered that restrictions were brought in after he took power in 2000, so his first term should not count.

Senegal's top legal body in late January approved Wade's candidacy, triggering a wave of clashes between rock-throwing protesters and police firing tear gas and rubber bullets in which at least six people have been killed.

Sall, 50, is a former Wade protege who held several high level posts, including minister of energy and mines, minister of the interior, and prime minister, before falling out with Wade and resigning his posts in 2008.

He was among several opposition figures active in Senegal's M23 protest movement, named after an anti-Wade riot on June 23 last year, that organised near-daily demonstrations in the run-up to Sunday's vote.

Wade, a veteran of years in opposition before he took power in 2000, has touted infrastructure projects including new roads and an airport as major achievements. But he has been criticised for not doing enough to improve the lives of ordinary Senegalese, particularly in the capital.

Washington has said Wade's decision to run again was regrettable, while Paris has said it was time for Senegal's younger generation to take power.

Some 5.1 million Senegalese were eligible to vote for the 14 contenders in the election. Apart from some polling stations opening late Sunday, voting appeared to have gone smoothly, according to a national network of observers.

(Additional reporting by Mark John, Diadie Ba, Bate Felix and Richard Valdmanis in Dakar; Writing by Richard Valdmanis; Editing by Louise Ireland)