Bomb Blast on Bus Kills 4 in Philippine Capital

At least four people were killed and 15 injured when a bomb exploded on a crowded bus in the Philippine capital's financial district on Tuesday, authorities said.

The attack occurred two months after the United States and several other Western governments warned a terrorist attack in Manila was imminent, and followed a bus hijacking last year that left eight Hong Kong tourists dead.

"The explosive must have been placed underneath the passenger seat," Metropolitan Manila police chief Nicanor Bartolome said on ANC television.

The explosion happened on Tuesday afternoon as the bus travelled along one of Manila's busiest roads, on the edge of the Makati financial district.

Vice President Jejomar Binay, a former mayor of Makati, arrived quickly at the scene and said it appeared to be a powerful blast.

"There's a huge hole and the debris indicates it is a bomb," Binay said, adding the legs of one injured woman had been blown off.

Police investigators were seen scouring the scene for evidence, with blood drying on the pavement.

The driver, who survived the attack unscathed, said at least two men who acted strangely quickly got off the bus just moments before the explosion.

"They were moving from one seat to another although we had no idea there was an explosive aboard," the driver, Maximo Peligro, told reporters.

"It could not have been mechanical... it was very strong."

He said about 30 people were on board the bus when the blast hit.

In November, the U.S., Australian, British, Canadian, French and New Zealand governments updated their travel advisories to the Philippines to warn that terrorist attacks were likely.

Some of the warnings specifically mentioned that an attack would take place in Manila.

Philippine President Benigno Aquino strongly criticized the advisories, saying they were not based on firm intelligence, prompting some of the governments to downgrade the threat assessment.

However, the U.S. maintained its warning, which could be viewed on its Manila embassy's website on Tuesday.