Police suspect that sparks from a welding torch might have started the fire yesterday in a kids' play area in the mall in Dongtan, a commuter town south of Seoul.
Two of the four who died were builders and the others were a mall worker and a shopper. Most of the 47 injured complained of smoke inhalation.
The play area was closed at the time of the fire.
Fire authorities urged builders to follow safety regulations, noting that welding torches were blamed for past blazes.