Six labourers were asphyxiated to death as they slept inside a locked bakery where a fire broke out early on Friday, the city police said here.The blaze, believed to be caused by an electrical short-circuiting, was noticed around 5.45 a.m. inside the Bakes and Cakes Bakery in Kondva area, an official said.Shanu Ansari, 22, Zakir Ansari and Fahim Ansari, both 24, Junaid Ansari, 25, Irshad Khan, 26, and Nishan Ansari, 28, all from Bijnaur district in Uttar Pradesh, were caught unawares in sleep as the flames and thick smoke quickly engulfed the mezzanine floor where they were sleeping.Rescue officials said the owner had locked the bakery shutter from outside, trapping and killing the workers inside besides seriously hampering the rescue and relief work.The bakery is located on the ground floor of a multi-storey building in a busy area of the city.Shaken by the tragedy, a Pune civic official said they would probe the conflagration and conduct a survey of all bakeries in the city to check their fire-preparedness and related issues.