Mr Modi congratulated Mr Kejriwal and promised him complete support.

Mr Kejriwal's anti-corruption Aam Aadmi Party (AAP) is leading in 63 of the 70 seats, while Mr Modi's Bharatiya Janata Party is ahead in only four seats.

The AAP is led by former tax inspector and activist Arvind Kejriwal.

Correspondents say his win would mark a remarkable comeback for the campaigner.

Mr Kejriwal's party was routed by the BJP in May's general elections, months after the AAP made a spectacular debut in the 2013 Delhi elections.

On the other hand, Mr Modi has enjoyed huge popularity since taking office last year, winning a string of local elections and wooing international investors and world leaders, and the BJP's defeat in Delhi is his first setback.

The BJP's campaign was essentially anti-AAP and the party leaders often criticised Mr Kejriwal at their rallies and road shows.

Mr Kerjiwal, meanwhile, conducted an energetic campaign which proved popular with working class and underprivileged voters who make up 60% of Delhi's population.

Mr Modi's Bharatiya Janata Party (BJP) fielded former policewoman Kiran Bedi as its candidate for chief minister.

"We never expected that the results would be so depressing. We never expected that we would suffer such a setback. It is certainly not our day today," BJP leader Praveen Shankar Kapoor told BBC Hindi.

The Congress party, which ran the Indian capital for 15 years until 2013, has suffered a complete rout and is not even leading in one seat.

Delhi has been without a government since Mr Kejriwal resigned last February as chief minister, angered that his anti-corruption bill was blocked.

Since then the state has been governed directly by the federal authorities.

(BBC News)