Vietnamese authorities said Saturday that a fire at a shoe factory in the northern port city of Haiphong killed 17 people and seriously injured another 21.

Police said the fire is believed to have been started Friday afternoon by welding equipment. The building had only one exit and the fire spread so fast that many workers were not able to escape.

Officials said 13 people died of burns and smoke inhalation at the scene and four other badly-burned victims died at a hospital Saturday morning.