Nepal's Maoist former rebels took a surprising early lead on Saturday in an election aimed at cementing a peace deal that ended a decade-long civil war.

Of seven results declared till Saturday morning the Maoists won five seats. They were leading in more than half of 102 constituencies where counting was on, election officials said.

The final result of the polls, Nepal's first in nine years, could take around 10 days.

A running tally of votes showed Maoist chief Prachanda and other senior Maoist leaders were ahead of their rivals. Some prominent leaders from other political parties were trailing.

"They have surprised themselves," an Asian diplomat said of the Maoists, whose victories so far have come from areas not known to be their stronghold.

"Even they had not expected this and every one thought that Maoists will be third. Nobody understands," he said.

"They have very intelligently chosen their candidates from different marginalised and ethnic groups."

Trends of results from the country's southern plains, home to nearly half of Nepal's total population, have yet to come. The Maoists are thought to be weak here.

Maoists say people had voted for a change and for a "new vision".

Some of their political rivals agreed.

"I think people want to give the Maoists a chance and test," Bhagwan Karki, a Communist UML party worker, said.

"Maoists spring a surprise, take initial lead," said a banner headline in the Himalayan Times.

Nepal went to the polls on Thursday to choose a 601-member special assembly tasked with mapping the impoverished nation's political future and formally ending the 240-year-old monarchy.

The elections were the main demand of the Maoists during their deadly civil war, which killed more than 13,000 people.

In 2006, they signed a peace deal with the government and entered electoral politics.

Analysts and diplomats said it is still too early to say if the Maoists will clinch a majority.

"The trends don't reflect how they would do in the proportional elections," said a Western diplomat, who asked not to be named.

He was referring to the complex election process - 240 members of the assembly are to be elected on a first-past-the-post basis, 335 on proportional elections and the rest named by the cabinet.

During the war, Maoists controlled huge swathes of the desperately poor countryside where basic services like roads, piped water, primary healthcare, education, electricity and telephones are lacking.

"Nepali people are looking for economic, social, cultural and political changes ... and a lasting peace," senior Maoist leader Krishna Bahadur Mahara said after being declared a winner.

"For this, they look to us as an alternative force," he said.