A suspected motorcycle bomb killed one person and wounded six others in a huge blast at a drugstore in the southern Philippines on Tuesday, police said.

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 Islamist militants linked to the Al-Qaeda movement, whose global leader Osama bin Laden was killed in a US military raid in Pakistan on May 2.

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