The Philippine military has found 21 bodies in the country's normally restive south -- the result of what appears to be politically-motivated violence.

Gunmen hijacked a convoy of about 30 politicians, their supporters and journalists Monday in the south as they travelled to file nomination papers for next year's election.

Thirteen women and eight men were among those shot to death dead, Col. Romen Brawner told The Associated Press.

The bodies were found in Ampatuan province, about five kilometres from where they were taken hostage.

It was unclear whether there were any survivors. An army and police search was still underway Monday for the remaining hostages.

The group had been travelling in three vans when they were stopped by about 100 armed gunmen, according to a military spokesperson.

Though the identities of the attackers has not been confirmed, the violence was blamed on the politicians' political rivals.

It was described as "unequaled in recent history" by Jesus Dureza, an advisor to Philippines President Gloria Macapagal-Arroyo.

"There must be a total stop to this senseless violence," Dureza said, recommending that a state of emergency be imposed in the area to disarm all gunmen. "Anything else will not work."

Among the dead was the wife of Ismael Mangudadatu, the vice-mayor of Buluan township. Her two sisters were also killed, along with local journalists and supporters.

The group was en route to Shariff Aguak township to file nomination papers for Mangudadatu to enter the race for governor of the province.

Mangudadatu himself was not on the bus.

At least 10 local reporters were with the convoy, according to the National Union of Journalists of the Philippines.

They have not been reached since, prompting speculation that there may be more fatalities.

"Never in the history of journalism have the news media suffered such a heavy loss of life in one day," Paris-based media watchdog Reporters Without Borders said in a statement.

The southern Philippines is often violent at election time as armed Muslim groups fighting for self-rule and warlords who keep their own private armies tend to flex their muscles.

A national election is scheduled for May 2010.