The incident took place when rival supporters turned up at the same time at a polling station at Aghalokpe, in the Olupe local government area, around 100 kilometres (60 miles) southwest of the oil town of Warri, in Nigeria's troubled Delta State.

It is not yet known which parties the youths were supporting.

The BBC's Jim Fish: "These elections should usher in civilian democracy next year"

Witnesses, all residents of the village, told the AFP news agency that police guarding the polling station had intervened but had not been able to stop the shooting immediately.

Voting was cancelled at the polling station, they said.

However, in most of Nigeria, voting went ahead peacefully on Saturday with millions voting across the country and in the Delta.

The BBC correspondent in Nigeria, Barnaby Phillips, says that with up to 40 million registered voters, the poll was an enormous challenge to the authorities. The turnout was said to be high.

Progress in these elections will give a clear indication of how well next year's national elections will go.

The elections are the first stage in the military government's plan to restore the country to civilian rule by next May.

Slow start

Saturday's voting got off to a slow start in many areas, with some polling stations not having received the necessary equipment more than an hour after they were supposed to open.

The BBC's Barnaby Phillips: Voter enthusiasm appears to be high

Initial reports suggested that the elections had on the whole passed off peacefully.

Nigeria's biggest city, Lagos, was reported to be very quiet. There were some delays in the capital Abuja and in the Northern city of Kaduna, but no serious disturbances. The oil town of Warri in Southern Nigeria was also reported to be calm despite threats of violence between the two main communities there.

Barnaby Phillips: "the electoral commission has passed its first test"

The nine parties contesting the election have to secure at least 5% of the vote in two-thirds of Nigeria's 36 states in order to contest January's state elections and February's national election.

The intention is to try and oblige political parties to attract support across the deep ethnic and regional divides of Nigerian society.

But correspondents say although many of the parties have sought to form national alliances, they have scarcely touched on the issues that affect ordinary Nigerians - including corruption, deteriorating social services and the perennial shortage of fuel.

'Play by the rules'

Nigeria's most democratic elections in years

Speaking on the eve of the poll General Abdulsalami Abubakar, Nigeria's military leader, called on politicians to avoid cheating and to play by the rules. He said politicians had to learn to believe that end does not justify the means.

General Abubakar, who has promised to hand over power to an elected ruler on 29 May next year, urged voters to turn out for the vote.