The trial of a Philippine clan accused of murdering 57 people in the country's worst political massacre will be broadcast on national television, the Supreme Court said Tuesday in a landmark ruling.

The court's decision came after repeated pleas by the victims' relatives, who fear the still powerful family could influence the trial, and was welcomed by President Benigno Aquino.

"We thank the Supreme Court. They finally listened to our plea. It is important that the entire nation learns how this thing happened," Aquino told reporters.

The court's ruling was unprecedented as no trial of a criminal case has been broadcast live, Filipino lawyers told AFP.

The court had ruled twice previously to ban live broadcasts of the trial, which began nine months ago, on grounds it could deprive the defendants of their right to a fair hearing in the politically charged case.

Andal Ampatuan Snr, the ex-governor of the southern province of Maguindanao, his son and namesake, plus four other relatives, are among more than 80 people held without bail and charged with the 2009 murders.

The Ampatuans, who had ruled Maguindanao for a decade, are alleged to have ordered the massacre to stop a rival from challenging Andal Ampatuan Jnr for the post of provincial governor in last year's elections.

Both father and son have pleaded not guilty to the murders, 32 of whom were journalists traveling in a convoy with the rival's family to an electorate office.

The Ampatuans had ruled Maguindanao under the patronage of then president Gloria Arroyo, who rights groups said allowed the clan to keep a large private army as a proxy force against Muslim rebels.

Hearings in the trial are being held twice a week in Manila. The Supreme Court did not say when the live broadcasts would start.

Victims' relatives have expressed concern that, in the Philippines' notoriously overburdened justice system, the trial could take years or even decades to complete.