Bus explosion in the Philippines

Reportedly, the explosion was so powerful it left several fist-size holes in a nearby concrete wall. The Indonesian President said last year the intelligence had received warnings from extremist groups they were plotting bombings.

The police chief officer of the Metro Manila said the explosion was caused by an improvised explosive device, placed under a passenger seat somewhere in the middle of the bus.

"We have declared full alert here in the National Capitan Region, this is to ensure that all of our policemen will be available and that vital instillations will be properly secured," he said.

Two officials said fragments of what appear to be a mortar round and cell phone parts were recovered at the scene.

The driver said he smelled gunpowder and the explosion was so loud his hearing was impaired for about 30 minutes.