A judge will decide Monday whether to uphold a corruption conviction against the leader of India's largest Tamil party, a verdict that could end the career of one of the country's most powerful and colourful politicians.

Jayalalithaa Jayaram was found guilty last September of amassing illegal wealth while in office and the former film star was sentenced to four years in jail in a case that ran for nearly two decades.

Jayalalithaa was forced to step down as chief minister of the prosperous southern state of Tamil Nadu, but she has continued to control her party while on bail awaiting the outcome of the appeal.

Monday's decision, however, could end the political fortunes of the 67-year-old who enjoys huge popularity in Tamil Nadu, where fans know her simply as "Amma" (Mother) and ministers have been known to prostrate themselves before her.

Security was tight in the southern city of Bangalore, with scores of supporters descending on the High Court ahead of the verdict, waving placards and chanting Jayalalithaa's innocence.

Additional Commissioner Alok Kumar said a cordon has been thrown around the court complex and several hundred extra police deployed in case of violence.

"The cordon will be in force from 6 o'clock in the morning till 6 o'clock in the evening," Kumar told the NDTV network.

In Chennai, the capital of Tamil Nadu, supporters were holding religious ceremonies in temples, praying for her conviction to be overturned, while scores were gathered outside Jayalalithaa's house.

Jayalalithaa has always dismissed the corruption charge, first brought by a rival politician in the state in 1996, as politically motivated.

She was charged in 1997, when police seized assets including 28 kilos (62 pounds) of gold, 750 pairs of shoes and more than 10,000 saris in a raid on her home.

Prosecutors said her assets, which reportedly included two 1,000-acre estates in the lush tropical state she ran, were vastly disproportionate to her earnings during her first term as chief minister, which ran from 1991 to 1996.

Jayalalithaa has earned the loyalty of many voters in Tamil Nadu with a series of highly populist schemes including an "Amma canteen" that provides lunch for just three rupees (five cents), although she has also drawn accusations of an autocratic governing style.