Polling for 32 assembly seats and the lone Lok Sabha constituency in Sikkim began simultaneously at 7 am on Friday.
Voting is scheduled to end at 5 pm.
Over 464,000 voters are eligible to exercise their franchise to elect their representatives in the assembly and an MP for Lok Sabha from the Himalayan state.
A total of 146 candidates, including Chief Minister Prem Singh Tamang, his predecessor Pawan Kumar Chamling, former footballer Bhaichung Bhutia, and Tamang's wife Krishna Kumari Rai are in the fray for 32 assembly constituencies.
Tamang and Chamling are contesting from two assembly constituencies each.
Voting is underway in 573 polling stations, out of which 88 are in urban and 485 in rural areas, Sikkim Chief Electoral Officer D Anandan said.
Thirteen companies of CAPF have been deployed in Sikkim, of which five companies are from ITBP and eight from SSB, he added.