Governor Kovind, 71, is a long-time BJP worker. He has served twice as a Rajya Sabha member and is a trained lawyer. He said PM Modi called him on Monday morning to inform him that he was the BJP's presidential candidate. After landing in Delhi, he met with the PM and Mr Shah.

The selection of a Dalit leader for President is a move by the BJP to consolidate its growing support among backward castes and poorer voters. If elected, Governor Kovind will be India's second Dalit president after KR Narayanan, who served from 1997 to 2002.

The opposition has said that despite the BJP talking of wanting a "consensus candidate", it sought no input on Governor Kovind's candidature. Opposition leaders will meet on Thursday to decide whether they will field their own candidate.

"Now that they have made the decision unilaterally, there is no more scope for discussion with them," said Left leader Sitaram Yechury, complaining that at conferrals last week, the BJP mentioned no names including that of Governor Kovind.

The complaint on not being consulted was duplicated by the BJP's permanently disgruntled ally, the Shiv Sena, which said it learnt through the media of the nomination for President.

Several opposition leaders are already indicating that they will find it tough to oppose Mr Kovind, given his caste. "As he is a Dalit, we are positive on his name, but only if the opposition doesn't announce a popular Dalit name (too)," said Dalit leader Mayawati.

Bihar Chief Minister Nitish Kumar, another key component of the opposition, said the Governor's credentials are also impressive. "Kovind has discharged his duties in an unbiased manner as the Bihar Governor. He has worked as per the Constitution and upheld the dignity of the Governor's post," the Chief Minister said after congratulating Mr Kovind in person.

However, he said, his party will decide on whether to back the Governor's promotion only after it consults with others on Thursday.

Ms Banerjee, the Bengal Chief Minister who has been a vocal critic of the PM on most issues lately, said, "I am not for a moment saying that the Bihar Governor Ram Nath Kovind is unfit to be the President. I have spoken to two or three other Opposition leaders, they are also surprised. There are other big Dalit leaders in the country."