Chief Insp. Jomar Yap, Philippine National Police-Region 12 spokesperson, said the explosive was planted by still unidentified inside the Weena Bus terminal compound and went off at around 11:05 am.
Another report said the bomb exploded at the ticket booth.
But Lt. Gen. Rodolfo Obaniana, chief of the military's Eastern Mindanao Command (EastMinCom), said Guinaid Adam, manager of the store and eatery inside the terminal told probers that a woman had earlier asked permission to leave her bag. "Minutes later, he received a bomb threat through phone".
Adam went to inform the police in the nearest Police Precinct 1 when he heard the explosion. The blast was traced to the bag left by the woman.
"Several stalls were damaged. Victims were rushed to the hospitals. Our troops are on high alert there," Yap said in a telephone interview.
Rushed to the Cotabato regional hospital were Ali Abdullah; Muslimin Abdullah; Bankunian Antungan; Monera Bakarat; Nida Budlaw; Alma Clarito; Ian Celis; Chona Delmonte; Aina Gubatbakarat; Zainal Kaanapia; Sukarno Kanudso; Abdulbasser Khalid; Guindo Kinon, Akmad Mamalimping; Kamis Marquez; Oscar Mimbala; Gubat Mohaimen; Odin Mustapha; Joel Pajarillo; Mike Rubise; Narina Rubite; Samy Sara; Wilma Tandog; Melanie Tanga; Ronald Tocao; Charles Spephen, and Adrian Tangao.
Tangao passed away. Radio station DXMS, however, identified the child as Adrian Bangao.
The explosion came less than two weeks after another bomb attack in the region. On May 8, a powerful blast rocked Tacurong City in Sultan Kudarat province, killing three people and wounding 30 others.
Authorities blamed the Tacurong attack to the Jemaah Islamiyah, listed by the United States government as a foreign terrorist organization.
Yap said Weena, the largest bus company plying the Davao City-Cotabato City route, has been the subject of attacks from extortionists in recent years.
At the moment, bomb experts are determining what kind of explosive was used in the fresh attack for authorities to be able to establish the group behind it, he said.
"Through the investigation, we will know if it has the signature of terrorists or just plain extortionists," he added.
The bombing came on the heels of the warning issued by the United States and Australia to its citizens against traveling to Mindanao due to possible terrorist attacks in the island.