India's Communist parties have swept to power in two Indian states as votes are being counted following elections that lasted a month.
The Communists won a record seventh term in West Bengal
A communist alliance won a record seventh term in West Bengal and has wrested Kerala from the Congress Party.
Separately, Congress Party President Sonia Gandhi has been re-elected in Rae Bareilly - she had quit parliament in March after a political row.
Her party is hoping to retain Assam and form a government in Tamil Nadu.
The southern state of Tamil Nadu appears headed for a coalition government even as early results indicated that the ruling AIADMK has been voted out.
The AIADMK is led by a former actress-turned politician, Jayalalitha - one of India's most controversial leaders - and is trailing behind its rival DMK which is leading in about 100 seats.
But it looks like it will fall short of an absolute majority in the 234-member state assembly and may have to form an alliance with the Congress which is leading in more than 30 seats.
In West Bengal, the Communist-led Left Front government is celebrating its historic victory - it is already the world's longest running elected communist administration.
"We had the people's complete trust and we knew we would win by a huge margin," Biman Bose, the West Bengal secretary of the Communist Party of India (Marxist), told Reuters.
The Communists back the federal Congress-led Indian governing alliance but oppose the party at the state-level.
Analysts believe that the Communist-victory in Kerala and West Bengal could spell trouble for the Congress because the left parties oppose several of its economic policies including increasing foreign investment and privatisation.
But the party is celebrating after the massive win of its president Sonia Gandhi in the parliamentary constituency of Rae Bareilly, which is a family stronghold and was once represented by the former Indian prime minister, Indira Gandhi.
Sonia Gandhi won comfortably in Rae Bareilly
Mrs Gandhi won the seat by a margin of 417,000 votes over her nearest rival - her margin in the 2004 parliamentary election was 250,000.
"It is the people of Rae Bareilly who have contributed to this victory," her son, Rahul, told journalists in the northern Indian town.
She quit parliament in March, following a controversy over her role as head of the National Advisory Council, a state-funded body set up to advise the current government.
Under Indian law, MPs may not gain financially from other public posts.
Vote counting is also taking place in neighbouring Pondicherry, which was once a French colony, and the north-eastern state of Assam where the governing Congress Party is ahead of the rival Asom Gana Parishad, although it may fall short of an outright majority.