The referendum Sunday in the Bolivian province of Santa Cruz - which seeks more autonomy from the rest of the impoverished country - was marked by violence that left at least 21 people injured before the end of voting, the dpa reported.
The referendum is part of a power struggle between Bolivia's poor, indigenous majority and the wealthier Bolivians of European descent who populate the eastern part of the country, including relatively affluent Santa Cruz province.
A reporter for Deutsche Presse-Agentur dpa and another journalist were attacked by pro-autonomy forces as they tried to interview a member of the Movement Towards Socialism (MAS) of left-wing Bolivian President Evo Morales.
The most serious incidents took place in the poor neighbourhood Plan 3,000, in the regional capital Santa Cruz. The neighbourhood holds some 200,000 residents, many of them from western Bolivia.
One of the injured, Laureano Rosa Fernandez, told dpa that he held the right-wing Union Juvenil Crucenista responsible for the attacks against him and others, and that both sides threw stones at each other.
Several people were stabbed, and one suffered life-theatening wounds in the clashes.
Morales regards the Union Juvenil Crucenista as street troops for the pro-autonomy movement.
According to the regional electoral authority, there was violence in seven of the 268 voting centres in the region, but only some 3 per cent of the voters were expected to be unable to vote. Mario Parada, head of the regional electoral authority, blamed the violence on the central government.
Bolivian central electoral authorities have deemed the referendum illegal and warned that they would neither monitor nor acknowledge the results, but opinion polls estimate that more than 70 per cent of the voters in Santa Cruz will cast a ballot favouring greater independence.
Morales supporters burned ballot boxes Saturday in Yapacani and San Julian in the first sign of potential violence over the vote.
At the heart of the confrontation is control of the region's rich natural resources, and issue has been brought to a head by Morales' ongoing nationalization of Bolivian's energy resources.
The issue is so heated that observers are not prepared to rule out a break-up of the landlocked country of 9 million people, in the Andes between Brazil, Argentina, Chile and Peru, over the conflict.
Tension has been growing since Morales, a former leader of Bolivian coca growers, was elected in late 2005 as the country's first indigenous president.
Morales began nationalizing Bolivian energy resources two years ago to pay for government programmes in support of the Indio majority, who live mostly in the resource-poor western highlands.
The government announced Thursday that it had taken over four international energy companies and would also take control of a telecommunications firm.
The referendum is to be followed by ballot questions in June in two other provinces also seeking greater autonomy.