Mexican presidential candidate Josefina Vazquez Mota went on the attack against her higher-polling rivals on Sunday in the second and final debate ahead of a July 1 vote that could see the once dominant Institutional Revolutionary Party (PRI) returned to power.

Mota, the candidate of President Felipe Calderon's National Action Party, said the other contenders represented a return to the country's corruption and authoritarianism, a past often associated with the PRI.

She accused frontrunner Enrique Pena Nieto, the PRI's candidate, of using public funds to create a spy agency and of hiding in a bathroom when students protested a May campaign appearance that has sparked a large protest movement, including a demonstration hours before Sunday's debate that drew 90,000 people to the streets of Mexico City.

"Mr. Pena Nieto, we don't want someone who is going to hide in the bathroom of a university to solve the country's problems,'' Vazquez Mota said.

Pena Nieto denied he was hiding and said he applauded the awakening of student participation in the political process. "It's a voice I respect,'' he said. 

The more than two-hour debate was held in Guadalajara, Jalisco, a state hard-hit by drug-related violence. The top two rivals - Pena Nieto and leftist Andres Manuel Lopez Obrador, who lost by a narrow margin in 2006 - hoped to get a boost from the event that could take them over the top.

Gabriel Quadri of the New Alliance party, who is polling in single digits, also took part in the debate in which the candidates made a flood of promises to create jobs, increase salaries, improve education, lower violence and end hunger without real details.

"There is a need for a new course that will translate into better living conditions for Mexicans," said 45-year-old Pena Nieto, who now has a commanding lead with 43.6 per cent support in polls to Lopez Obrador's 29.2 per cent.

Vazquez Mota trails in third place, with polls giving her 25.3 per cent support. She is the country's first female contender for president for a major party.

Root out corruption

Lopez Obrador said he would save millions by rooting out corruption and cutting politicians' salaries, numbers that Vazquez Mota said didn't add up.

She in turn emphasised her role as a woman and caretaker of the family and mentioned several times her support for indigenous women.

Pena Nieto repeated several times that Mexicans would be able to provide for their families in the manner they deserve under his administration.

"The centre of my proposal is that you earn more,'' he said.

Pena Nieto's PRI ruled for 71 years before being voted out in 2000, but Mexican voters appear ready to reject PAN after 12 years of Vicente Fox and Calderon, who launched an assault on drug cartels and whose term has seen more than 47,000 deaths from drug violence.

Negative advertising has increased in the last two weeks among all three major parties - the PRI, the PAN and Lopez Obrador's Democratic Revolution Party.

The race has also sparked a nationwide protest movement, I Am 132, a reference to the 131 students who went public on the internet after Pena Nieto's campaign responded to his embarrassing May appearance at Iberoamerican University by claiming the student hecklers had been planted by rival campaigns.

Nearly 80 million Mexicans are eligible to vote for a new president for a six-year term beginning in December. The election will also renew the lower and upper houses of the Congress and select governors in six states, the Mexico City mayor and local legislative bodies.