At least five people were killed, including a 4-year-old child, while 38 others were injured in a massive explosion at a pyrotechnics depot in the southern Philippines, local authorities said Sunday.

The Saturday afternoon blast at the Zamboanga City site tore a large hole in the ground, sent debris careening into nearby buildings and houses and ignited a blaze, fire investigator Luigi Chan told the Agence France-Presse (AFP).

Four warehouse workers and the 4-year-old son of one of the staffers were killed, Chan said.

The city disaster office confirmed the death toll and said another 38 people had been injured in the incident, eight of them seriously.

Authorities said they are investigating the cause of the explosion, which created a 20-meter (66-foot) crater, dismantled the depot's walls and rained rubble on a nearby soft drinks factory, a grains and flour warehouse and area homes.

"The most probable origin of the fire is the pyrotechnics stored at the warehouse," Chan told AFP.

He said the blast radius extended more than 3,000 square meters (0.8 acres) and it took firefighters more than two hours to bring the blaze under control.