Electoral commission chief Abdullah al-Buainain insisted: "We are determined that the elections should be transparent," adding that polling stations would be monitored by 379 observers from Bahraini non-governmental organisations.
But opposition groups have warned of the dangers of fraud while rights groups have said the polls are unlikely to meet basic conditions for fairness.
In a challenge to the ruling Khalifa family's long domination of political life, the leader of the mainstream Shiite opposition in parliament called openly during the election campaign for an end to its hold on the premiership and other key levers of power.
"It is unacceptable that power be monopolised by a single family, even one to which we owe respect and consideration," the head of the Islamic National Accord Association, Sheikh Ali Salman, told a mass rally in a suburb of the capital Manama late on Wednesday.
Despite the 2002 reforms which renamed the then emirate a constitutional monarchy and restored the legislature dissolved in 1975, King Hamad's uncle, Sheikh Khalifa bin Salman al-Khalifa, has served continuously as prime minister since independence from Britain in 1971.
"We look forward to the day when any child of the people, be they Sunni or Shiite can become prime minister," Salman told the campaign rally.
Mindful of the government's crackdown on radical reformers which will see 23 Shiite opposition activists go on trial -- two in absentia -- on terrorism charges next week, Sheikh Salman was careful to stress that he was not seeking to subvert the regime.
"We are not defying anyone's authority. It's a political goal that we are working to achieve through legal and political means," he said.
Unlike the radical groups which continue to boycott Bahrain's electoral process, Sheikh Salman's grouping is contesting 18 of the 40 seats in parliament in this weekend's election. It held 17 in the outgoing legislature.
In the election run-up, the prime minister issued a stern warning to anyone seeking to challenge the current constitution.
"It is unacceptable for anybody to call into question something that was unanimously approved by the Bahraini people," Sheikh Khalifa told Bahraini newspapers.
During the campaign, the authorities detained 250 Shiite opposition activists, London-based watchdog Amnesty International said earlier this month.
Its New York-based counterpart Human Rights Watch called on Washington to speak out in favour of reform in Bahrain which is the home base for the US Fifth Fleet.
"What we are seeing in Bahrain these days is a return to full-blown authoritarianism," said the watchdog's deputy Middle East director Joe Stork.
"The government has taken over associations and shut down media it doesn’t like to silence the loudest critics and intimidate the rest, and Washington says nothing publicly.
"Under the current circumstances, it is hard to see how these elections will meet basic conditions for fairness -- such as freedom of expression and association," Stork said.
The 2002 constitution was adopted in the wake of deadly unrest among the Shiite majority through the 1990s.
-----------------------------------------------------------------------------