An email threatening bomb blasts at Amitabh Bachchan's bungalow, Chhatrapati Shivaji Maharaj International Airport and the Mumbai Mayor's office forced authorities to place the city on high alert.

The message cited dates November 27 and December 31, and mentioned a supposed organisation called "Khalistan National Army".

Similar threats had reached officials earlier this year, targeting the mayor's office and other venues. In response, security levels were raised and searches carried out citywide.