Cotabato City (Philippines) : A powerful bomb apparently rigged to a vehicle exploded on a busy main road in a volatile southern Philippine city, killing at least eight people and wounding more than 30 others, officials said.

Troops and police closed off the area along Sinsuat Avenue in Cotabato city as firefighters and ambulances arrived at the chaotic scene during the Monday afternoon rush. Witnesses saw at least four people bloodied on the pavement as cars and buildings burned after the explosion.

The fire damaged power and telephone cables, causing power outages nearby, police said.

City police chief Senior Superintendent Rolen Balquin, said Tuesday that two victims had died overnight in the hospital, raising the death toll to eight. He said the dead included a police officer.

At least 33 people were wounded by bomb shrapnel and flying debris from cars and motorcycles damaged by the explosion, he said. Several were in serious condition among 13 who remained in the hospital Tuesday, he said.

Cotabato, a bustling trading hub 880 km south of Manila, has been hit previously by bombings blamed on Muslim rebels and extortion gangs.

The bomb exploded Monday afternoon as a bulletproof SUV carrying city administrator Cynthia Guiani-Sayadi was passing by. She was not hurt but one of her police bodyguards in a security van was killed, officials said.

Balquin said they were looking at the possibility the attack could have targeted Guiani-Sayadi, a younger sister of Mayor Japal Guiani. He said the city administrator “had been receiving threats for the past few days.”

Mayor Guiani said they have witnesses who have pointed to possible suspects and the mastermind of the attack but he declined to identify them.

National Police chief Alan Purisima ordered regional and provincial police offices in the southern Philippines to step up intelligence and security, particularly for soft targets such as commercial areas and other places where people converge, said police spokesman Senior Superintendent Reuben Theodore Sindac.

President Benigno Aquino III’s administration condemned the bombing and vowed to hunt down those responsible.

“We condemn the use of violence to kill and maim our countrymen who are peacefully going about their daily lives,” Aquino’s spokesman Herminio Coloma said. “We’ll hold accountable these criminals who terrorise our society.”

Philippine authorities did not immediately point to any suspects, but government forces have been on alert in the volatile region due to recent attacks and bombings by a breakaway Muslim rebel faction opposed to peace talks between the government and a main insurgent group.