NUKU'ALOFA - The people of Tonga voted to elect a majority of parliamentarians for the first time in the impoverished South Pacific island nation's history Thursday, another step in a decades-long struggle to throw off aristocratic rule.

Tongan King George Tupou V described the vote as "the greatest and most historic day for our kingdom" in an address to the nation before polling stations opened.

The election, however, did not reflect full democracy as nine nobles -- the country's aristocratic landowners -- will be chosen by the king for the country's 26-seat parliament. Some observers warned the nobles could control the new parliament if they enter an alliance with a handful of lawmakers elected by the public.

The election comes after Tonga suffered major political unrest in 2007 when rioters demanding democratic change torched the centre of the capital, Nuku'alofa, burning down buildings and killing eight people.

The moribund economy was seen as the most pressing issue for Tongan voters. The World Bank estimates up to 40 per cent of Tonga's 100,000 people live on or below the poverty line.

"People are saying we're very concerned about what we feed ourselves with, our future, how much we get paid, whether we can have the ability to put our kids to school," said voter Kalafi Moala. "The economy is definitely the priority."

Lines for polling stations began to form early Thursday as some of the 42,000 registered voters went to fill out their ballots for 146 candidates.

Veteran pro-democracy campaigner Akalisi Pohiva's grouping grabbed eight of the 10 seats on the main island of Tongatapu, according to preliminary results released by the nation's electoral office. Results for the seven seats on other island groups of the archipelago were expected Friday.

Thursday's election means the prime minister will be elected by 17 lawmakers chosen by the people. The previous parliament had nine elected lawmakers, with the prime minister, Cabinet, and nine nobles appointed by the monarch.

The deadly riots and the 2006 death of King Taufa'ahau Tupou IV -- one of the world's longest serving monarchs -- fueled moves by his son, King George Tupou V, to relinquish power.