Two leading presidential candidates in Senegal say they do not accept unofficial results that show incumbent Abdoulaye Wade has won Sunday's polls.
The 81-year-old incumbent is seeking a second term in office
Partial results indicate that Mr Wade, 81, has more than 55% of the vote making a run-off unnecessary, Senegal's official news agency reports.
But Ousmane Tanor Dieng and Abdoulaye Bathily say there were irregularities.
Analysts say that it will be surprising if there is no second round, given the mood in the country before polling.
A candidate needs to gain more than 50% of the vote to avoid a second round.
A commission at the appeals court has until Friday to announce the official results.
Senegal, a predominately Muslim nation, is seen as a rare model of stable democracy in Africa.
Observers from regional body the Economic Community Of West African States have said the voting on Sunday was free and fair.
The BBC's Tidiane Sy in the capital Dakar, says most Senegalese were expecting there to be a second round.
"We will not accept these results," Aissata Tall Sall, Mr Dieng's spokeswoman, told a press conference.
The Socialist Party leader Mr Dieng, who served under the previous president, Abdou Diouf, has been seen as a strong contender.
His party, which was in power for four decades prior to Mr Wade's victory in 2000, said some people had been allowed to vote more than once.
"These results do not reflect the feelings of the population which, in reality, expressed a massive rejection of Abdoulaye Wade's authority," AFP news agency quoted leftist leader Mr Bathily as saying.
Voter turnout was high and long queues left some polling stations open late.
Events since Sunday have been somewhat chaotic, with a series of claims and counter-claims about the results.
Mr Wade, who is seeking a second term, has come under pressure in recent months over high rural unemployment.
Since his election he has fallen out with several of his allies, some of whom were among the opponents challenging him on the ballot papers.
Mr Wade's campaign manager has urged the president's 14 opponents to concede defeat.
Observers say the voting was free and fair
But the other contenders say they will wait until official results are released before commenting, our reporter says.
A run-off would present an opportunity for Mr Wade's opponents to team up against him.
That is exactly how the president came to power seven years ago in one of Africa's rare peaceful transitions from one president to a rival.
It is the only West African nation not to have experienced a coup since independence, and polls in 2000 passed off peacefully.
Some five million people were eligible to vote, which is almost double the figure in the last election.