Initial reports said the bus, which bears plate number MWB-296 and body number 2008, was traversing a secluded stretch of the national highway in Barangay Glammang at around 12:00 noon when the IED went off.
Investigators said the explosive was placed in the baggage compartment at the seventh row of the bus.
Witnesses said the 19 wounded passengers sustained shrapnel wounds from the explosion.
Three of the passengers identified as Jerryl Cabuyao, his wife Abigail, and their seven-day-old baby Akisha Gale were rushed to St. Elizabeth Hospital in General Santos City.
The South Cotabato Rescue Team identified the other 16 passengers injured in the blast as Mark Anthony Dela Cruz, Mary Grace Villaseran, Rose Villamarie Talusi, Ericka Maulin, Omar Solani, Cecil Amelier, Princess Olarte, Twinkle Mae Olarte, Elnam Olarte, Marilou Yabut, Divina Duran, Amor Pedrigosa, Francis Eric Resticia, Angel Ayoc, Ebona Canua and Moises Fajartin.
All 16 were taken to the General Santos Doctors Hospital for treatment.
Authorities are still conducting post blast investigation to the identity group behind the blast but local officials believe extortion is the motive behind the bombing.
Meanwhile, another blast was reported around 1:00 p.m. today at Barangay Sunrise in Isabela City, Basilan, killing three people.
SecurityMatters sources said exploded just outside the main gate of the compound of Mayor Cherrylyn Santos-Akbar.
Initial investigation revealed that the bomb exploded while the two-vehicle convoy of Vice Mayor Abdulbaki Ajibon was passing by.
Two of Ajibon’s staff who were aboard one of the two vehicles in the convoy were killed in the blast while Gregorio Heneral Delgado, a bystander, was also killed.
Local police chief, Supt. Albert Larubis, said the bomb could have been placed in a tricycle parked on the roadside where the blast happened.
Investigation is ongoing to determine the motive and identify the suspects behind the bombing.