MUMBAI: Mumbai police stepped up security on Thursday to prevent any unrest as Indian firebrand politician Bal Thackeray was reported in a “very critical” condition in hospital.

Large crowds of supporters gathered overnight outside the home of ailing 86-year-old Thackeray, who founded the right-wing Hindu party Shiv Sena and is widely accused of stoking communal tensions in the city.

“We have a lot of forces on the roads. Extra measures are being taken,” Mumbai police spokesman Nisar Tamboli told AFP.

In the early hours of Thursday, Thackeray's son Uddhav emerged from the residence 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 will power. 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 earlier told the agency that Thackeray's condition was “very critical” and that he was on a life support system.

Bollywood veteran Amitabh Bachchan and his actor son Abhishek were among those to visit Thackeray's home in the night, where they were 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.

Thackeray is one of the best-known and most controversial figures in the western state of Maharashtra and its capital, which his party renamed from Bombay to Mumbai.

The Shiv Sena became synonymous with deadly communal violence during its campaign to protect local Marathi-speaking people and their culture from migrant workers.