Seventeen factory workers were killed and 21 seriously injured after they became trapped in a burning Vietnamese shoe workshop that did not have a fire escape, according to local police. The fire is believed to have been started by welding equipment on Friday afternoon at the unlicensed business in the northern city of Haiphong, the head of the police in An Lao district, Phan Xuan Lai, told AFP. \"We arrested six people for investigation straight away,\" he said. The flames spread so quickly that those inside could not get out of the building fast enough. \"It had only one very small exit and was located in a narrow road,\" Lai explained, adding that it took an hour to extinguish the fire. Ten of the victims were women, including two younger sisters of the Vietnamese woman who owned the workshop with her Chinese husband. \"Four of the workers have died this morning in hospital,\" Lai said. The workshop had been operating for just four months and employed more than 40 workers, he added. Deadly fires are common in Vietnam and are generally blamed on a lack of fire-safety measures.