Itanagar, Oct 13 - Voting for 57 of the 60 assembly seats in the northeastern state of Arunachal Pradesh opened Tuesday morning amid tight security, officials said.

An election official said voting began at 7 a. m. in the 57 seats with three candidates already declared elected unopposed.

Chief Minister Dorjee Khandu and two more ruling Congress members - sitting legislator Tsewang Dhondup from Tawang constituency and debutant Jambey Tashi from the Lumla seat - were declared elected unopposed.

Khandu was elected unopposed from the Mukto constituency in Tawang district, bordering China, in the 1999 and 2004 assembly elections as well.

A total of 157 candidates are in the fray with the ruling Congress party fielding candidates in all the seats.

An estimated 750,000 voters are eligible to exercise their franchise with voting taking place in 2,000 polling booths in the state.

The fight for political supremacy would be between the ruling Congress party and a fractured opposition - two of them, the NCP and the Trinamool Congress, allies of the Congress-led United Progressive Alliance government in New Delhi, and the Bharatiya Janata Party (BJP).