Police in Luc Ngan District of Bac Giang Province, which borders Hanoi, said the incident occurred Monday when three boys, aged 13, 15 and 17, were creating the firecracker from chemicals they bought online.
The explosion killed the 13-year-old and left the other two injured.
The case is being investigated further.
Vietnam has banned the production, sale, and burning of firecrackers and explosives nationwide (except for fireworks) since Jan. 1, 1995 after the use of fireworks became rampant, causing many deaths and injuries and annual losses of tens of billions of dong. (VND10 billion = $436,400)