A Philippine court has frozen bank accounts and other assets belonging to a powerful political clan accused of being behind the country's worst political massacre, officials said Wednesday.

The 20-day writ that took effect on Monday froze assets worth at least a billion pesos ($23 million), said Vicente Aquino, executive director of the central bank's Anti-Money Laundering Council.

The order covers bank accounts, financial investments, houses and vehicles, said lawyer Dionisio Jimenez, who manages the records of the Court of Appeals.

"It's a freeze order, which means they cannot withdraw or dispose of the those assets," Jimenez, officially designated as court clerk, told AFP.

Andal Ampatuan Snr, the former governor of Maguindanao province, and five relatives were among more than 80 people arrested and charged with murder over the 2009 massacre of 57 people in the Muslim clan's southern stronghold.

The Ampatuans, who had ruled Maguindanao for a decade, are alleged to have ordered the murders to stop a rival from challenging one of the clan patriarch's sons for the post of Maguindanao governor in last year's elections.

The victims, who included 32 journalists covering the electoral challenge, and some of their vehicles were found buried in mass graves in Maguindanao.

The patriarch and his son Andal Ampatuan Jnr have pleaded not guilty to the charges. More than 100 other suspects remain at large.

Aquino, no relation to President Benigno Aquino, said the council goes after funds that it suspects were illegally acquired, but declined to discuss the suspected origins of the Ampatuan assets.

"These would be worth more than a billion pesos in all," Aquino told AFP.

Most of the cars and properties are now in government control, but the bank accounts are protected by a strict Philippine bank secrecy law which only a court order can open, Jimenez added.

"They (the government) would have to file a forfeiture case with the regional trial court if they want to get hold of the funds," Jimenez said.

The appelate court is to hear shortly a government petition to extend the freeze beyond 20 days, he added.