Six labourers were killed and three others injured after part of an under-construction bridge collapsed following a storm over the Betwa river in Uttar Pradesh's Hamirpur district early Friday, officials said.The incident occurred around 3 am between Parsani and Kandaur villages when a slab of the bridge being constructed from Maurakandar to Kurara collapsed, they said. According to officials, several labourers engaged in the bridge construction work were sleeping on the upper portion of a slab when it suddenly gave way.