Nine of the injured are in serious condition, local authorities said.
Police have questioned the truck driver, a man in his 60s, who claims the truck malfunctioned. Witnesses have told investigators that the vehicle first backed up about 28 meters and then drove forward for 150 meters, hitting pedestrians. Footage from the scene shows, among other things, that the truck crashed into a shop window and caused widespread damage.
The driver was not under the influence of alcohol or drugs, according to Bucheon police.
Bucheon is located near the capital Seoul.
