Around 14 labourers were working in the five-storey building, located at Hindustan Compound, when it caught fire around 4.00 AM, Circle Officer, Cantt area Sushil Dhule said.
Of them, two received serious burn injuries and were rushed to a nearby private hospital where doctors declared them brought dead, he said.
The deceased were identified as Shivbali (50) and Sushil (22) while a few others also received minor burn injuries, he said.
Atleast 12 fire tenders were rushed to the spot and took over six hours to control the blaze, he said.
The cause of the fire is yet to be known, SSP Kanpur Shalabh Shrivastava said, adding that losses have not been assessed.
The tannery owner will be questioned in this regard, the SSP added.