An unidentified person called up Sir HN Reliance Foundation Hospital in south Mumbai on Wednesday and threatened to blow it up, a police official said.
"The caller also issued threats in the name of some members of Ambani family," he said.
The person called up the hospital's landline number at 12.57 pm from an unknown number, the official said.
An FIR has been registered at DB Marg police station against the unidentified person and an investigation is on into the matter, he added.
In August this year, a jeweller was arrested after he allegedly calling up the hospital and threatened to kill industrialist Mukesh Ambani and his family members.
In February 2021, a sports utility vehicle (SUV) laden with explosives was found near Ambani's south Mumbai residence 'Antilia'.
Later, some people, including the then-police officer Sachin Waze, were arrested in connection with the incident.