COTABATO (Philippines) • Two people were killed and about 35 others wounded after a bomb went off outside a shopping mall in the southern Philippine city of Cotabato, police said yesterday.

Monday's explosion prompted officers to search the mall, leading to the discovery of another suspected bomb which they destroyed, said police spokesman Chief Inspector Rowell Zafra.

A female street vendor and one man were killed, while many of the injured were people shopping for the New Year. Three of the wounded were in critical condition.

Windows of buildings in the vicinity of the mall were shattered by the explosion, eyewitnesses said.

Investigators could not yet say what kind of bomb was used. Local army commander Cirilito Sobejana told ABS-CBN television that an individual was seen carrying a box which he left in front of the mall. It exploded a few seconds later.

Major-General Sobejana said the bomb had the signature of a "Daesh group", referring to militants who have declared allegiance to the Islamic State in Iraq and Syria (ISIS).

The southern part of the largely Catholic Philippines has been rocked for decades by violent Muslim separatist insurgent groups including militants linked to ISIS.

More than 100,000 lives have been claimed by the rebellion, according to a government count.

The region has also suffered from banditry, bloody clan feuds and communist guerilla activity.

Bombs went off in Isulan town, 77km south of Cotabato, killing at least three people, last August and September. The authorities said the main suspect in these blasts was the pro-ISIS Bangsamoro Islamic Freedom Fighters armed group.

Monday's bombing came ahead of a plebiscite in the southern Philippines this month for the creation of a Muslim autonomous area as part of an attempt to end the separatist insurgency. Many of the ISIS-linked groups have rejected these peace efforts.

Cotabato Mayor Cynthia Sayadi said that despite the bombing, "we will try to assure the people that... their right to vote (in the plebiscite) will be protected".

President Rodrigo Duterte put the southern Mindanao region under martial rule until the end of last year after pro-ISIS militants seized the city of Marawi in 2017. Martial law has been extended to the end of this year.