Bahraini voters are taking part in the country’s first parliamentary elections since Arab Spring protests broke out in 2011.
The government has called on all of the country’s political factions to participate in Saturday’s poll.
But Shia opposition groups plan to stage a boycott, saying the vote is an attempt to establish “absolute rule”.
Despite being ruled by a Sunni monarchy, the majority of the Bahraini population are Shias.
Disenchanted protesters took to the streets of the capital, Manama, in 2011 to demand greater civil rights.
But the protests were stamped out when the government, backed by Saudi tanks, moved in to crush dissent.
Talks to resolve the situation have since collapsed and unrest has continued.
Some 350,000 people are eligible to vote, choosing 40 legislators from among 266 mostly Sunni candidates.
A coalition of opposition groups said it would boycott Saturday’s legislative and municipal elections.
The alliance, which includes al-Wefaq, Bahrain’s most popular opposition group, has called the poll a “sham”.
It has also demanded an elected prime minister who is independent from the ruling al-Khalifa monarchy.
“These elections are destined to fail because the government is incapable of addressing the political crisis,” al-Wefaq member Abdul-Jalil Khalil told the Associated Press news agency.
Bahraini Information Minister Sameera Ebrahim Bin Rajab said that the “door to dialogue will never be shut, including with al-Wefaq” but added: “Violence is not allowed. It is tantamount to terrorism.”
Bahrain is of key strategic importance to Washington and hosts the US Navy’s 5th Fleet.
The election will also be closely watched by Saudi Arabia, which has a large Shia Muslim population in its Eastern Province.