The explosion at about 3.15 p.m. at a scrap metal trading business tore through several houses and left a large crater in Van Phu residential area, Ha Dong District.
According to initial reports, a worker were trying to cut open an oxygen cylinder when it exploded. The worker and three passers-by, including a 7-year-old girl, were killed immediately. Many other people were hospitalized with multiple injuries.
A report on the Vietnam Plus website quoted Colonel Vuong Tien Dung, police chief of Ha Dong District, as saying that he could confirm at least four deaths.
"It's not clear whether the explosion was caused by gas or explosive," he was quoted as saying.
The blast blew out the windows of about 20 neighboring homes and caused several fires. It could be heard from 4 kilometers away, witnesses said.