Halfway into the ballot count on Thursday, television reports indicated that the BJP was way ahead of the Congress in the two huge Hindi-heartland states of Madhya Pradesh and Rajasthan.
In Madhya Pradesh, the BJP was leading in 177 of the 230 seats as against 33 for the ruling Congress.
In the 200-seat Rajasthan assembly, the party had secured leads in 117 seats compared to 59 for the Congress at 2:00 pm (08:30 GMT).
But in the capital Delhi, the Congress by early afternoon had secured leads in 49 of the 70 seats, followed by the BJP at 17.
The central tribal state of Chattisgarh, however, was heading for a close finish with the BJP, leading in 52 of the 90 seats and the Congress in 36.
The final results were expected later on Thursday, but were not expected to differ much from the trends, reports said.
The four states where the assembly polls were held were all ruled by the Congress party.
"I think if the BJP wins three states, there would be renewed pressure on Vajpayee to hold early elections"
The handsome gains for the BJP, after a long spell of crushing defeats, also revived talk of early parliament polls.
But BJP leaders said the elections due by October would not be brought forward.
"There is a choice between a summer and September election. I am 100% sure they will be on schedule," party general secretary Pramod Mahajan said.
Vote for change
Madhya Pradesh Chief Minister Digvijay Singh, who has been in power for 10 years, conceded defeat.
"I think the people have voted for a change, let them have a
change," he told reporters.
Electoral officials said 53.2 million - or 57% - of about 94 million eligible voters - cast their ballots in the four states.
The results, if confirmed, will mark the most significant winning spree by the Hindu nationalists since they came to power at the national level in 1999.
"You have seen the development work that has been done here, my priority will be to take this ahead"
Delhi chief minister
Since then, the party has lost state after state to the Congress except in communally polarised Gujarat and the tiny state of Goa.
This week's poll is seen as a barometer of support for the BJP and the Congress before the parliamentary elections.
Analysts said voting took place largely on local issues such as water, power and roads and not on any national issue or personality.
On Wednesday, Prime Minister Vajpayee told his party MPs to
begin preparing for parliamentary polls, but gave no indication that they would be brought forward.
Speculation about polls
But his call to prepare for the polls triggered intense speculation about the timing of general elections.
"I think if the BJP wins three states, there would be renewed pressure on Vajpayee to hold early elections," political analyst
Mahesh Rangarajan said.
However, political sources said that "Vajpayee wants to complete a full five-year term and go down in history as the only non-Congress prime minister to have done so".
Also, there is a huge risk of a setback if the party dissolves parliament before putting its house in order in the crucial northern states of Uttar Pradesh and Bihar, where it is in a shambles, the sources added.
Vajpayee also wants to give a serious "last bid" at peace with