An Indian court has sentenced the chief minister of the southern state of Tamil Nadu to four years in prison for corruption in a case that was filed 18 years ago.

J Jayalalithaa had been charged with amassing illegal wealth of at least $10m in 1997, when police seized assets including 28 kilogrammes of gold, 750 pairs of shoes and more than 10,000 saris in a raid on her home.

The judge held Jayalalithaa "guilty of amassing wealth disproportionate to known sources of her income," prosecutor G Bhavani Singh told reporters outside the court earlier on Saturday.

She was sentenced to four years in jail a few hours later. NDTV, a private television channel, reported that Jayalalithaa had been taken for a mandatory medical check-up before being sent to prison.

Jayalalithaa would lose her position as the chief minister since Indian law prohibits any politician from holding public office after being sentenced to more than two years in jail.

Prosecutors said her assets, which reportedly included two 1,000-acre estates in Tamil Nadu, were vastly disproportionate to her earnings during her first term as chief minister between 1991 to 1996.

"I think it's very difficult for her to escape it because the facts are very clear. She claimed a salary of one rupee per year and ultimately amassed in five years, 66 crores [one crore equals 10 million rupees]. How is that possible?" said Subramanian Swamy, the leader of rival Bharatiya Janata Party and the main complainant in the case, before the court ruling.

"So therefore it is an open and shut case and she is likely to be convicted and ceased to be chief minister."

The 66-year-old Jayalalitha, a former film star who became one of the country's most colourful and controversial politicians, enjoys huge popularity in Tamil Nadu, a manufacturing hub.

Her All India Anna Dravida Munnetra Kazhagam party emerged as the third biggest force in the national parliament after winning 37 of the 39 parliamentary seats in the state in this year's general election.

Indian politicians are seldom convicted for corruption and even more rarely end up spending time in jail.