Lucknow, May 31 (IANS): In a major set back to the ruling BJP in Uttar Pradesh, its candidate is trailing in the high-stake Kairana parliamentary constituency, the counting for which is underway on Thursday, an official said.

After the fifth round of counting, Bharatiya Janata Party's Mriganka Singh was trailing by over 6,200 votes as Rashtriya Lok Dal's (RLD) Tabassum Hasan maintained her lead.

"These are early trends and we are sure that we will emerge victorious in the final outcome," a senior BJP functionary told IANS.

Hasan has been supported by the Samajwadi Party (SP), Bahujan Samaj Party (BSP), Aam Aadmi Party (AAP), the Congress and the regional Nishad Party in the bypoll which was held on Monday.

Kairana's trends are being watched closely across the country as this could set in motion the opposition unity if its candidate wins and could undo the victory march of the BJP, which had earlier lost the Gorakhpur and Phulpur seats in the state.

District Election Officer Indra Vikram Singh said the postal ballots were counted first after which phase-wise EVM's were being counted.