The blast occurred as the four adults were attempting to strip fireworks to make explosives for use in fishing, the official Chinese news agency Xinhua reported.
Han Jinghua, deputy head of the security bureau, said authorities were going door-to-door to confiscate illegal explosives like the kind a local fisherman and his workers were using that triggered the blast.
Local authorities have been asked to erect warning signs near rivers forbidding the use of explosives for fishing.
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