Police investigators inspect the area of a market where an explosion happened in Davao City. Lean Daval Jr., Reuters

MANILA - Police now have custody of eight witnesses and several CCTV clips that could shed light on the deadly Friday night explosion in Davao City.

Chief Inspector Andrea dela Cerna, spokesperson of the Davao police regional office, said Sunday that the witnesses linked four "persons of interest" to the bombing that killed at least 14 people.

READ: Improvised bomb caused Davao blast, police say

In a bid to identify the persons of interest, dela Cerna said investigators continue to gather CCTV footage from establishments around the bombed night market in Roxas Avenue.

The police Criminal Investigation and Detection Unit has a CCTV clip from the blast site itself, but it was not clear, she explained.

The Philippine National Police has yet to confirm that Abu Sayyaf extremists were behind the attack.

Dela Cerna said they were looking into the possible role of "disgruntled vendors" in the explosion. Some traders, she said, were dissatisfied with the granting of stalls in the night market.

The Davao bombing, which also injured at least 67 people, has prompted President Duterte to declare a "state of lawlessness" in the country.

Embassies of the United States, United Kingdom and Australia have also advised their citizens to either reconsider or avoid travel to the southern Philippines due to the incident.