Illegal manufacturing and storage of detonators triggered an explosion in a residential building of Baoding City in north China's Hebei Province, which has left one killed and 34 injured by Sunday morning, local police said.

Police found self-made detonator shells at the explosion site of the six-storey building in Dongwuyao Village. Detonator shells and materials of explosives were also discovered in the building's basement.

Police suspected illegal manufacturing and storage of detonators might have caused the blast.

The injured have been sent to hospital for treatment. Among them, two remained in critical condition, said a spokesman with the city government.

Part of the building collapsed after the blast happened at around 3 p.m. at the Yaoheningyuan Residential Community in Baoding.

Witnesses said heavy smoke was seen following the explosion, which shattered window glass of buildings 200 meters away.

An overhaul of illegal storage of explosives has been staged across the city following the blast, police said.