A bombing wounded 33 people during an amateur boxing match in a central Philippines province, the government said on Thursday, the second attack on a public place by unknown perpetrators in less than a week.

An 81-millimetre mortar round was detonated remotely by cellphone during the amateur bout outside a shopping mall in Leyte province late on Wednesday. Police said no suspects had been identified and no group had claimed responsibility.

It followed a Christmas Eve grenade explosion outside a Catholic church that wounded 16 people on the southern island of Mindanao, a Muslim-dominated region where a long-running insurgency is being fought.

Police said there was no indication the two attacks were linked.

President Rodrigo Duterte has warned of the threat of a proliferation of festering Islamist militancy in the Philippines and an infiltration by the Islamic State militant group if offensives to drive its fighters out of Iraq and Syria succeed.

Duterte has warned of vulnerability in the southern Philippines, where some splinter groups have pledged allegiance to Islamic State and only a small stretch of sea separates predominantly Muslim areas of the Philippines, Malaysia, Brunei and Indonesia.