A smiling ex-Philippine president Gloria Arroyo pleaded not guilty on Thursday in her first court appearance since being charged with rigging an election, an offence that could see her jailed for life.

Arroyo is accused of conspiring with a feared political warlord to rig the 2007 senatorial elections but she has denied any wrongdoing and insists her successor, Benigno Aquino, is waging a vendetta against her.

'Not guilty,' Arroyo, 64, told the judge after standing up in a Manila courthouse wearing a neck brace to support her spine that she says is weakened from a rare disease.

Arroyo had smiled and waved to a crowd of journalists after she arrived at the court from a military hospital where she had been detained for nearly three months while awaiting trial.

She smiled again after leaving the brief arraignment hearing and heading back to the hospital in a police convoy, but did not talk to reporters. No trial date was set.

The vote-rigging case is the first of many charges Aquino has promised to file against his predecessor, whom he has accused of many corrupt acts while she was in power from 2001 to 2010.

Prosecutors allege Arroyo ordered that ballots in 2007 elections be switched in the southern province of Maguindanao so that one of her allies won the final position available in the nation's senate.

Arroyo is alleged to have conspired with then-Maguindanao governor and close political ally Andal Ampatuan Snr to tamper with the ballots.

Ampatuan Snr, who had a reputation as a ruthless political warlord, is a co-defendant in the vote-rigging case.

He is also facing multiple murder charges for allegedly organising with his relatives the massacre in 2009 of 57 people in Maguindanao to stop a rival's election challenge, an event that forced Arroyo to end their alliance.

Aquino, the son of democracy heroes, won a landslide election victory in 2010 on a vow to fight corruption that has plagued Philippine society for decades but he said worsened dramatically during Arroyo's reign.

Arroyo has been the top target of his anti-graft campaign.

But three weeks after Arroyo's arrest, Aquino's allies in the lower house of parliament also impeached Supreme Court chief justice Renato Corona on charges of corruption and protecting the ex-president.

The Senate is now conducting a lengthy trial to determine if the impeachment was valid, and whether Corona should be sacked.

In a speech on Tuesday, Aquino warned his anti-corruption efforts hinged on successful prosecutions of Arroyo and Corona.

"If certain elements are still able to prevent Gloria Arroyo, for example, from being held accountable, then it makes a mockery of our anti-corruption efforts," he said.

"We want to send a stern yet simple message: justice evades no one. There are no exceptions in our campaign against corruption."

Aquino was arrested at an exclusive hospital three days after immigration authorities stopped her at Manila's airport from leaving the country.

Arroyo's lawyer said then her spinal disease was life-threatening, and the Supreme Court under Corona issued an order saying she was allowed to leave the country for treatment.

But Aquino insisted Arroyo was trying flee to evade prosecution and that she was not allowed to leave.

Arroyo, the country's second female president, who is now a congresswoman after winning a parliamentary seat in the 2010 elections, was transferred to the military hospital shortly after her arrest.

She was hit with a second criminal charge in December in relation to a $330-million telecom deal with a Chinese firm, in which her husband and a political ally allegedly received kickbacks.