86-year-old Shiv Sena chief Bal Thackeray has been put on life-support and is in "very critical" condition, doctors treating the politician told PTI.
As the news spread, several hundred party workers assembled outside his residence 'Matoshree' in suburban Bandra, where security has been stepped up.
Speaking outside the residence, Sena leader Ramdas Kadam said, "Doctors are trying their level best (to stabilise Mr Thackeray's condition) and conducting some tests on him."
Mr Thackeray's nephew, Raj, who was estranged from him till recently was at Matoshree, where the Sena leader resides with his son Uddhav. A number of Shiv Sena MPs, legislators and senior leaders also visited the house.
Actor Amitabh Bachchan and his son Abhishek were among the visitors. Mr Bachchan's kurta
was torn according to some reports as he tried to make his way into the house through the huge crowd.
Actor Sanjay Dutt and his wife Manyata also met Mr Thackeray's family late on Wednesday night.
Police have set up barricades near Matoshree to streamline the flow of crowds.
A team of doctors stationed inside the house with nursing staff has been taking care of the Sena patriarch, who has been having breathing problems recently.
Last month, he could not attend his party's annual Dussehra rally in Mumbai, but addressed it through a video recorded message.