Fears of militia violence and calls for a boycott are threatening to marr Libya's first nationwide parliamentary election.

The election is a milestone on the oil-rich nation's rocky path towards democracy after the ousting of dictator Muammar Gaddafi.

The vote for a 200-member transitional parliament caps a tumultuous nine-month transition towards democracy for the country after a bitter civil war that ended with the capture and killing of Gaddafi in October.

Many Libyans had hoped the country would quickly thrive and become a magnet for investment, but it has suffered a virtual collapse in authority that has left formidable challenges. Armed militias still operate independently, and deepening regional and tribal divisions erupt into violence with alarming frequency.

On the eve of the vote, gunmen shot down a helicopter carrying polling materials near the eastern city of Benghazi, the birthplace of the revolution, killing one election worker, said Saleh Darhoub, a spokesman for the ruling National Transitional Council. The crew survived after a crash landing.

Prime minister Abdurrahim el-Keib vowed the government would ensure a safe vote and condemned the election worker's killing and those who sought to derail the vote.

"Any action aimed at hindering the election process is against the supreme interest of the nation and serves only the remnants of the old regime," he said. "It is threatening to the future of the revolution and its accomplishments ... and an attempt to stop democracy for which Libyans sacrificed their souls."

It was not immediately clear who was behind the shooting, but it was the latest unrest in a messy run-up to the vote that has put a spotlight on some of the major fault lines in the country - the east-west divide and the Islamist-versus-secularist political struggle.

Nearly 2.9 million Libyans, or 80% of those eligible to vote, have registered for the election and more than 3,000 candidates have plastered the country with posters and billboards. Polls are to be open from 8am to 8pm local time, with results expected within a week.

There are four major parties in the race, ranging from the fundamentalist Muslim Brotherhood on one end of the spectrum to a secular-minded party led by a Western-educated former rebel prime minister on the other.