Mumbai police stepped up security on Thursday to prevent any unrest as Indian firebrand politician Bal Thackeray was reported to be in critical condition at his home in the city.
Large crowds of supporters gathered overnight outside the residence of the 86-year-old, who founded the right-wing party Shiv Sena.
"We have a lot of forces on the roads. Extra measures are being taken," Mumbai police spokesman Nisar Tamboli told AFP. Security was particularly tight around Thackeray's home.
President Pranab Mukherjee cancelled a visit to Mumbai on Thursday, local media said, though no official reason was given for the change in schedule.
Roads were unusually quiet and many shops were closed in the city, which has been celebrating the Diwali festival this week, with some people opting to stay at home or leave offices early.
In the early hours of Thursday, Thackeray's son Uddhav emerged from the house in the suburb of Bandra to reassure the crowds and ask them to pray for his father.
"We are hopeful. You be hopeful. Let's pray," he said.
"Bal... has strong willpower. We'll come out from the problem. Don't trust rumours. Make peace," he was quoted as saying by the Press Trust of India news agency.
Doctors on Wednesday night had said Thackeray was in a "very critical" condition and on a life support system, but Shiv Sena spokesman Sanjay Raut said on Thursday he was now stable.
"Need not worry. He is responding to doctors' efforts," Raut told PTI.
Bollywood veteran Amitabh Bachchan and his actor son Abhishek were among those to visit Thackeray's home in the night, where they suffered minor injuries in the rowdy crowds.
"Yes both Abhishek and me were injured with cuts, but are fine and back home," the elder Bachchan wrote on Twitter.
A television van was also reportedly damaged by Shiv Sena followers.
Thackeray is one of the best-known figures in the western state of Maharashtra and its capital, which his party renamed from Bombay to Mumbai.