Manila  - At least five people were killed in an explosion Thursday that rocked a firecracker factory just outside the Philippine capital, local officials said.

The blast occurred shortly before noon inside the Starmaker Fireworks factory in the village of Conchu in Trece Martires City in Cavite province, 25 kilometres south of Manila, according to Mayor Melencio de Sagun.

De Sagun said only two bodies of those killed remained intact while the other three bodies were found torn to pieces.

Alvin Mojica, vice mayor of Trece Martires, said more than 40 people were also reported injured in the explosion, a number of them in critical condition.

Mojica said thick smoke hampered the firefighters efforts to enter the factory.

The explosion was so powerful it destroyed the sprawling factory and glass panels of nearby buildings were shattered, according to Mojica.

Classes in elementary and high schools were suspended because of the tragedy.

Police have not yet established the cause of the explosion. (dpa)