The man identified as Imtiyaz, along with two other persons, went to Neelam Building on Park Street posing as Kolkata Municipal Corporation officials and tried to force their entry and tried robbing the family, the police said.
They hit an old woman residing in the flat with a hammer when she resisted them, a police officer said.
"Residents of the flat started shouting when the trio tried to run away. While the liftman tried to stop them the miscreants attacked him with a knife and injured him," he said.