India's Supreme Court today asked a Bharatiya Janata Party leader, who took oath as chief minister of the key southern Indian state of Karnataka on Thursday, to prove his majority in the state assembly tomorrow.

"Let the House (Assembly) decide and the best course would be floor test," said a three-judge bench of the top court headed by Justice A K Sikri.

Senior BJP leader B S Yeddyurappa, 75, was sworn in as the 23rd chief minister of Karnataka on Thursday by Governor Vajubhai Vala.

Senior lawyer Mukul Rohatgi, appearing for the chief minister, sought time from the apex court till Monday for the majority test but the bench, also comprising Justices S A Bobde and Ashok Bhushan, ordered it to be held tomorrow.

Vala invited Yeddyurappa to form the government on Wednesday evening and gave him 15 days to prove his majority on the floor of the House.

The BJP emerged as the single largest party in Karnataka state election but fell short of majority, triggering a close race for power between the party and its rivals Congress and Janata Dal (S).

The BJP won 104 seats in the 224-member assembly, nine short of a majority while Congress fell to 78 seats from 122 won in the previous election five years ago. It has offered to support Janata Dal (S) which got 37 seats.

Congress and Janata Dal (S) claim to have the support of two independents and have accused the BJP of trying to lure their legislators to switch sides.

The swearing in of Yeddyurappa was cleared by the top court bench after Congress party, which was voted out of power in last Saturday's election, tried to stop him being sworn in as chief minister by stitching up a last-minute coalition with JD (S).

Following a three-hour legal battle that started around midnight, the Supreme Court allowed the swearing in to take place.