Local amateur photographer, Gemana Ali, 53, was killed in the explosion, Superintendent Roberto Badian, the police chief of the southern city of Cotabato said.

A seven-year-old boy was in a critical condition in hospital.

"It appears the bomb was triggered by a cell phone," Badian told reporters, adding no group had claimed responsibility.

He said the remotely-triggered improvised explosive device was hidden in a motorcycle that had been abandoned near the drugstore and a gun shop.

"Initial reports (show) the explosives were kept inside a single motorcycle," said Chief Superintendent Benjardi Mantele, the police chief for the region.

Cotabato, a city of 164,000 people, has in the past been a target of Muslim separatists and militants linked to the al Qaeda movement.

The attack occurred as Cotabato, a Christian-Muslim trading post on the troubled main southern island of Mindanao, observed the second day of Ramadan.

Copyright AFP (Agence France-Presse), 2011