9/3/2106: A previous version of this story stated that a doctor, Leopoldo Vega, spoke to Al Jazeera by phone about the victims of the explosion. That was incorrect. He made the statement during a press conference.

A blast has ripped through a night market packed with customers in President Rodrigo Duterte's home city of Davao in southern Philippines, killing at least 12 people and wounding 60 others.

A presidential spokesman said on Friday that the blast took place at the open-air market in Davao City, 960km south of the capital, Manila.

The explosion occurred close to the high-end Marco Polo hotel that is popular with tourists and business people, city spokeswoman Catherine de la Rey told AFP news agency.

Regional police chief Manuel Guerlan told Reuters news agency that a ring of checkpoints had been thrown around the city's exit points.

A thorough investigation is being conducted to determine the cause of the explosion

Manuel Guerlan, Regional police chief 

"A thorough investigation is being conducted to determine the cause of the explosion," he said. "We call on all the people to be vigilant at all times."

Student John Rhyl L Sialmo told Al Jazeera that the explosion happened around 10:30pm local time (4:30GMT).

"We were inside one of the university buildings when we heard the loud explosion," Sialmo, a student at Ateneo de Davao University, said.

"There were so many people, because it was a night market and also because it's a Friday," Sialmo said, adding that "the rescuers had to use improvised bandages on the victims".

"One woman rushed to the university to ask for help and she said she saw bodies and body parts laying around," he said. "She looked very traumatised."

A doctor from the Southern Philippine Medical Center in Davao City said that all those who died had "multiple shrapnel injuries".

"All of the wounds examined were shrapnel type on different parts of the body," D Leopoldo Vega told reporters in a news conference.

"All the doctors were on call and everybody was with us here in the emergency room specifically for this disaster."

War on drugs

The Philippine president was in Davao, but was safe and at a police station after the explosion, his son Paolo Duterte, who is vice mayor of the city, told Reuters news agency.

Duterte is hugely popular in Davao, having served as its mayor for more than 22 years before his stunning national election win in May, garnered from the popularity of a promised war on drugs.

READ MORE: Death toll in Duterte's war on drugs

His election has prompted a spike in drug-related killings, with more than 2,000 people killed since he took office on June 30, nearly half of them in police operations.

Davao is located in Mindanao, a large southern island beset by decades of armed rebellion by Muslim groups. The region is also home to Abu Sayyaf, a rebel group loosely linked to Islamic State of Iraq and the Levant (ISIL also known as ISIS) and notorious for making tens of millions of dollars from kidnappings.

There was no immediate claim of responsibility.

However, Davao itself is largely peaceful and Duterte has been credited with transforming it from a lawless town to a southern commercial hub for call centres and offshore business processing services.

Source: Al Jazeera And Agencies