After spending nearly 70 years underground, the bomb was found at a construction site and sold to a salvage yard.
The ordinance was heavily rusted, keeping workers there from realizing what it was.
“We believe the bomb dates back to World War Two and weighed about 227 kg. As they probably did not know (what to do), “they used a blow torch to try to cut open the bomb,” police bomb squad chief, Kamthorn Auicharoen told Reuters.
The huge blast destroyed the scrap business in the Lad Plakao neighborhood of Bangkok. Seven people were thought to be killed, but the body of a four-year-old girl was discovered in the rubble later, upping the total to eight.
20 others were injured and buildings up to 500 yards away were damaged.
Both US and British warplanes dropped bombs on during World War II, when the area was under control of the Japanese army.