Laura Chinchilla thanked supporters for electing her as Costa Rica's first female president and only the fifth ever in Latin America, as her opponents accepted defeat.

The 50-year-old ruling party candidate joined thousands of supporters after first results showed she had won 47 per cent of the votes counted, way ahead of her main opponents and above the 40 per cent needed to avoid a run-off.

"Thank you, Costa Rica," Ms Chinchilla said in an address in a hotel in the capital, San Jose. "It's certainly a moment of happiness, but above all of humility ... I won't betray that confidence."

The Centre-left opposition candidate Otton Solis had won 24 per cent of the votes counted and Otto Guevara, a right-wing lawyer, garnered 21 per cent.

"With a lot of respect, we accept the reality," Mr Solis, who lost by a whisker to current President Arias in 2006, told a gathering of his followers earlier. Mr Guevara congratulated "our President Laura Chinchilla," shortly afterwards.

The opposition had criticised Ms Chinchilla as being a puppet of Mr Arias, a Nobel Peace Prize laureate, and she is expected to continue his policies of promoting free trade and international business ties.

The slight, long-haired graduate of Georgetown University in the United States served as vice president under Mr Arias and is socially conservative on issues such as abortion.

Her National Liberation Party (PLN) bet on her past experience as public security minister and justice minister to win voters over on the issue of crime - a growing concern here.

Voting took place calmly throughout Latin America's oldest democracy, which has no army, amid fears of high abstention rates.

Abstention was at 33.43 per cent, according to initial results, of some 2.8 million eligible to vote for a new president, two vice presidents, as well as 57 lawmakers and municipal leaders.

The elections again tested the organizational skills of the PLN, which has dominated politics in Costa Rica for the past six decades, and was expected to make gains among lawmakers too.

Ms Chinchilla was also aided by Costa Rica's relatively smooth passage through the global economic crisis, and by support from powerful economic sectors close to Mr Arias.

The mother of a teenage son has promised to increase grants for poor students, expand the pensions for the poor and open day-care centres to support working mothers.

Although she has vowed to bring in tougher anti-crime measures, she also underlined the importance of acting "intelligently" against crime caused by social inequalities.

She follows in the footsteps of four female presidents in Latin America - in Chile, Argentina, Panama and Nicaragua - in a nation which has promoted positive discrimination to bring women to political posts in recent years.

Mr Solis, an economist from the Citizen's Action Party, ran on an anti-corruption ticket and had lagged behind Mr Guevara, 49, who founded the pro-business Libertarian party.

Mr Arias is due to hand over to the new president on May 8.

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