Manila: A packed bus strayed into an oncoming lane and crashed into another bus on a highway south of Manila on Tuesday, killing at least 11 people and injuring 29 others.

Police investigator Allan Potong said authorities are trying to find out whether the driver of the first bus was sleepy while negotiating the road in Camarines Sur.

Eight people were killed on the spot, one passenger died on arrival in a hospital and two others died later, he said.

It was not immediately clear if the drivers were among the dead.