The candidate of the former ruling party is leading in early returns.

Mexico's former ruling Institutional Revolutionary Party, PRI, is set to return to power after 12 years as early official results indicated that its candidate, Enrique Peña Nieto won the presidential election. Nieto, 45, had about 37 per cent of votes late Sunday evening, several points ahead of Andres Manuel Lopez Obrador who had not conceded defeat, the BBC said.

Josefina Vazquez Mota, presidential candidate of the ruling National Action Party (PAN), got 25 per cent in the third place. A fourth candidate, Gabriel Quadri de la Torre of the New Alliance Party (Panal), got more than 2 per cent of the vote.

Celebrations at the headquarters of PRI started after the polls closed. The Los Angeles Times said the election commission figures were meant to be a representative sample of the nationwide vote. Shortly after they were released before midnight on Sunday, Peña Nieto appeared on television to claim victory. He thanked voters and said he would run a responsible presidency that is open to criticism.

Earlier, President Felipe Calderon had welcomed Peña Nieto as his successor. Calderon promised to work with him during the transition until the inauguration in December 2012. Observers say although the final results are to be announced after July 4, preliminary results always show high reliability in Mexico's election history.

The PRI party held on to power for 71 years until it was defeated in 2000. Peña Nieto built his reputation by focusing on public works and improvement of infrastructure. With nearly half of Mexicans living in poverty, the economy was one of the main issues in the campaign. Unemployment remains low at roughly 4.5 per cent, but a huge divide remains between the rich and the poor. Another issue that dominated the campaign was the war on drugs, launched nearly six years ago by President Calderon. Over 55,000 people have been killed in drug-related violence since 2006.