A POWERFUL EXPLOSION, believed to have been caused by a bomb, tore through a Catholic Mass, killing at least four people and injuring dozens of others in a predominantly Muslim city in the southern Philippines, officials said.

The Sunday morning Mass was under way in a gymnasium at the state-run Mindanao State University in Marawi city when the blast happened, causing panic among dozens of students and teachers and leaving the victims bloodied and sprawled on the ground, said Taha Mandangan, the security chief of the state-run campus.

At least two of the injured are fighting for their lives, he said.

“This is clearly an act of terrorism. It’s not a simple feud between two people. A bomb will kill everybody around,” Mr Mandangan told the Associated Press.

Regional military commander Major General Gabriel Viray III said at least four people were killed by the explosion, including three women, and 50 other people were taken to two hospitals for treatment of mostly minor injuries.

Only two of those killed have been identified, officials said.

Army troops and police immediately cordoned off the area and were carrying out an initial investigation and checking security cameras for any indication of who may have been responsible for the attack. Security checkpoints were set up around the city.

The deadly blast set off a security alarm beyond Marawi city as the Christmas season ushered in a period of travel, shopping sprees and traffic jams across the country.

The Philippine coast guard said it has ordered all its personnel to intensify intelligence-gathering, stricter inspections of passenger ferries and the deployment of bomb-sniffing dogs and sea marshals following the suspected bomb attack.

“Amid this barbaric act, best public service must prevail,” coast guard chief Admiral Ronnie Gavan said in a statement.