No candidate has secured an outright victory in Sunday's presidential election in Guinea-Bissau, the electoral commission has said.
A run-off vote between the top two contenders will be held next month.
Jose Mario Vaz, an ex-finance minister from the main PAIGC party, will face Nuno Gomes Nabiam, a military-backed bureaucrat running as an independent.
The general elections were the first since a coup in 2012, after which the EU and others suspended aid donations.
Guinea-Bissau has a history of coups and no elected leader has served a full term since independence from Portugal in 1974.
Guinea-Bissau is one of the poorest countries in the world and has been further destabilised by the booming trade in illegal drugs from Latin America, in which the country is used as a staging post for the European market.
In the first round, Mr Vaz took 41% of the votes compared to 25% for Mr Nabiam.
More than 80% of the electorate turned out to chose from 13 presidential candidates and 15 parties fielding candidates for parliament.
In the parliamentary vote, the PAIGC party, which has dominated politics since independence, won 55 of the 102 seats.
The Party for Social Renewal (PRS) of former President Kumba Yala, who died earlier this month, took 41 seats.
Mr Yala had not endorsed his own party's presidential candidate, instead backing Mr Nabiam, who is a former head of the civil aviation authority.
The PAIGC majority in parliament means the leader of that party's parliamentary list, Domingos Simoes Pereira, will become the next prime minister.
"These results, if managed well by particularly the leaders of the two main political parties, will ensure that Guinea-Bissau finally has the stability that is essential for structural reforms in all sectors," Reuters news agency quotes Jose Ramos-Horta, the UN special representative in Guinea-Bissau, as saying.
The presidential run-off is expected to be held on 18 May.
The West African nation has stagnated since 2012, under the rule of a transitional government backed by its all-powerful military.
With few resources other than cashew nuts and fish, South American drug cartels have turned the country into a cocaine-trafficking hub.
The money that generates has corrupted many of the country's public institutions, particularly its armed forces.
A year ago, the US charged 2012 coup leader Antonio Indjai with drug trafficking and seeking to sell surface-to-air missiles to Colombia's Farc rebels, to shoot down US patrol helicopters. He has not been extradited.