Gloria Macapagal Arroyo was president of the Philippines from 2001 to 2010 [Reuters]

Former Philippine President Gloria Macapagal Arroyo has pleaded not guilty to an electoral fraud charge at the opening of a landmark trial.

Arroyo was escorted early on Thursday under tight security to a Manila courtroom from a military hospital where she is being detained while undergoing treatment for a spine ailment.

"Not guilty," she said in court when asked to respond. If convicted, she could face life in prison.

After her appearance, which lasted only about 10 minutes, she was escorted back to the hospital.

She wore a neck brace and even managed to pose for souvenir photos with people in the courtroom, smiling and shaking hands with them.

Court spokeswoman Felda Domingo said the trial is historic because "the votes of the people were sabotaged and the accused is a former president".

Arroyo was president from 2001 to 2010. The case against her involves senatorial polls in 2007; she is accused of rigging the results to favour her candidates.

Her husband, Miguel Arroyo, called the case against his wife an injustice.

The case has emerged as a key test for her successor, President Benigno Aquino III, who has promised to root out corruption and said that no one should be allowed to evade justice.

The electoral sabotage charge is the first of several criminal cases being prepared against Arroyo.