Guyana's President Donald Ramotar says there will be an investigation into the deaths of at least three people during clashes between police and protesters.
Demonstrators protesting against rising electricity prices in the town of Linden said police had fired bullets and tear gas into the crowd.
During the clashes, several buildings were burned and the governing PPPC party said its offices were damaged.
Protesters say rampant poverty makes it impossible for them to pay more.
Opposition party Alliance For Change (AFC) said the unrest in Linden could spread to other parts of the country.
"These killings have taken us to a tipping point of serious and widespread social and civil unrest," an AFC spokesperson said.
Prime Minister Samuel Hinds said there had been a reduction in the electricity subsidy which drove up the prices.
But Mr Hinds said residents of Linden were no worse off than those of other towns.
"Linden is no more depressed, no less depressed, no more prosperous, no less prosperous, than many other places in Guyana," he said.
Correction 6 September 2012 : An earlier version mistakenly reported that protesters had burned down the offices of the governing party and an electricity plant.