Two persons were killed and twelve injured as a private six-storey building of cold-storage-cum-godown in the outskirts of Nagpur city collapsed last evening.Two bodies were extricated from the debris and several other injured people were taken out till late last night and the injured were rushed to the Indira Gandhi Medical College and Hospital for further treatment.The one and half year old building was still under construction in parts and use of the sub-standard building material could be one of the main reasons for the mishap.