No suspects have yet been identified in the blast on Thursday evening in Cotabato City, 960 kilometres south of Manila, according to Superintendent Willie Dangane, city police chief.

Dangane said the lone fatality was an entertainer at the nightclub, while the other victims were customers.

Police said the nightclub's owner and security guard were being questioned for clues on who could have lobbed the grenade and what could be the motive for the attack.

Chief Superintendent Felizario Serapio, a regional police commander, said investigators were looking into personal grudge as a possible motive.

'It's premature to link terrorist groups in the incident,' he said. 'Why inside the bar? It could be that a personal grudge is behind the attack.'

Government security forces have been on alert against terrorist attacks in the southern region of Mindanao since last month amid warnings from foreign governments.