Shiv Sena chief Bal Thackeray's health has turned "very critical" and he is on life-support system, doctors treating the Sena leader said.
As the news spread, several 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 Thackeray's condition) and conducting some tests on him."
MNS chief Raj Thackeray and close family members have reached Matoshree, where the Sena leader resides with his son Uddhav. A number of Shiv Sena MPs, legislators and senior leaders are also at Thackeray's residence.
Actor Amitabh Bachchan, considered close to the Thackeray family, and his actor-son Abhishek are also at 'Matoshree'.
Police have set up barricades near Matoshree to streamline the flow of crowds.
Thackeray, who is ailing for sometime, continues to be under constant medical supervision.
A team of doctors stationed inside the house with nursing staff has been taking care of the Sena patriarch, who is having breathing problems.
Last month, he could not attend his party's annual Dussehra rally in Mumbai, but addressed it through a video recorded message.
Several leaders, including former President Pratibha Patil, have visited Thackeray's residence over the past few days to enquire about his health.