Thackeray, 86, is in a "very critical" condition, doctors treating the Sena leader told a news agency.
As the news spread, several party workers assembled outside his residence, 'Matoshree', in suburban Bandra, where security has been stepped up.
Bollywood superstar Amitabh Bachchan along with his son Abhishek visited the Shiv Sena leader. Thackeray’s nephew MNS chief Raj Thackeray was also seen at ‘Matoshree’.
Thackeray, who is ailing for sometime, continues to be under constant medical supervision.
A team of doctors stationed inside 'Matoshree' 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.
Mumbai: The health condition of Shiv Sena chief Bal Thackeray turned "very critical" Wednesday night.
First Published: Wednesday, November 14, 2012, 11:11