Senegal's veteran leader Abdoulaye Wade faced the prospect Tuesday of a runoff election after conceding he may have failed to secure a first round victory in his bid to remain president into his 90s.

Although official results are not due until later in the day, Wade revealed on state television that early tallies showed him winning less than a third of the votes counted so far -- albeit with a clear lead over his nearest rival.

While Wade said that "everything is possible, victory or a second round of voting" ahead of official results, the opposition savoured its strong showing.

"Wade, its over," headlined L'Observateur opposition newspaper, calling the incumbent's address to the nation on Monday night his "swansong".

The United Nations and the United States meanwhile called for calm on all sides after the run-up to Sunday's ballot was marred by deadly violence.

Wade, 85, is seeking a third term in office after circumventing a two-term limit he introduced into the constitution. He says changes extending term lengths from five to seven years made in 2008 allow him a fresh mandate.

The country's highest court upheld his argument, sparking a month of riots that claimed six lives and prompted international concern for the west African nation's long-held reputation as a haven of stability.

In his television address, Wade said he would rise to the challenge of a second round, evoking the possibility of alliances to assure a final victory.

The president said that the results from around half the overall turnout gave him 32.17 percent of the votes. His closest challenger, former prime minister Macky Sall, had 25.24 percent.

Sall, 50, appears to be the most likely contender in a second round and called the results a "massive rejection of the outgoing president."

The mayor of the western city of Fatick fell out of favour in 2008 with Wade, his former mentor, under whom he had held several ministerial portfolios and also served as prime minister.

Election day passed off without any major incident and all sides are being urged to ensure the situation remains peaceful.

United Nations special representative in west Africa Said Djinnit urged the population to "show restraint until the end of the electoral process."

The United States' top Africa diplomat Johnnie Carson said "early results indicate that a second round of voting is highly likely".

"We call upon all political party leaders and their supporters to follow the rule of law and respect the results," Carson added.

Emerging market analyst Samir Gadio, with London-based Standard Bank said Wade had suffered a "setback" for Wade but he would still prevail if the opposition fails to present a united front.

"The outcome of the second round will be conditional on the opposition's ability to firmly unite behind one candidate and present a coherent platform for political change."

Wade, who is Africa's oldest leader after Zimbabwe's Robert Mugabe, 88, was first elected in 2000 on a wave of euphoria and his supporters praise him for overseeing a development boom.

However he was roundly booed as he cast his ballot and was trounced in his home polling station -- a sign of how his popularity has plunged amid efforts to cling to power and line up his unpopular son Karim to succeed him.

He is also accused of focusing on prestige projects and being out of touch with the needs of the people, battling high unemployment and crippling power cuts.

Both France and the United States urged him to retire as protests swept the nation, with angry youths clashing with police on a near-daily basis in the seaside capital.

However Wade dismissed the opposition against him as "temper tantrums" and heaped scorn on his former allies, saying he refused to be dictated to.

The former French colony of some 13 million people is one of the continent's pioneer democracies, boasting an unbroken series of elections since independence in 1960. Unlike many of its troubled neighbours it has never suffered a coup.