The call was received at the PBX of 'Nabanna' when the Chief Minister was present in her office on the 14th floor. Police was immediately informed of about the phone call, Joint Commissioner Kolkata Police (Headquarters) Supratim Sarkar said.
Kolkata Police, its bomb detection and disposal squad, dog squad, special branch, detective department along with Howrah Police and other security agencies immediately rushed to 'Nabanna' and conducted a thorough search on all the floors, Sarkar said.
Along with different floors, the roof of the building too was checked throughly by the bomb and dog squads, besides the parking and other places around the building.
The call turned out to be a hoax as nothing was found in the hours-long search operation, Sarkar said.
Security in and around the entire Secretariat has been beefed up following the incident, he added.