Opponents and supporters of Venezuela's President Nicolas Maduro planned to rally on Tuesday as protests and clashes spread after a weekend election was awarded to the long-ruling socialist despite opposition claims of a landslide victory.

Renewed instability in the South America oil producer brought divided international reaction: the United States said Maduro's reelection had no credibility and was mulling more sanctions, while China and Russia congratulated him.

Protests began after the election board declared on Monday that Maduro had won a third term with 51% of votes to extend his "Chavista" movement's quarter-century rule.

The opposition, which considers the election body in the pockets of a dictatorial government, said the 73% of vote tallies to which it has access showed its candidate Edmundo Gonzalez had more than twice as many votes as Maduro.

Many Venezuelans staged "cacerolazos", a traditional Latin American protest where people bang pots and pans in anger.

Some blocked roads, lit fires and threw petrol bombs at police as protests proliferated, including near the Miraflores presidential palace in Caracas.

"We are tired of this government, we want a change. We want to be free in Venezuela. We want our families to return here," said one masked protester, referring to the exodus of about a third of Venezuelans in recent years.

"I'll fight for my country's democracy. They stole the election from us," said another.

Police with shields and batons in Caracas and the city of Maracay fired tear gas to disperse some protests.

Many demonstrators rode motorbikes and jammed streets or draped themselves in the Venezuelan flag. Some covered their faces with scarves as protection against tear gas.

The government calls them violent agitators.

"We've seen this movie before," said Maduro from the presidential palace, pledging that security forces would keep the peace. "We have been following all of the acts of violence promoted by the extreme right."

The armed forces have long supported him and there were no signs generals were breaking from the government.

In Coro, capital of Falcon state, protesters cheered and danced when they tore down a statue depicting former President Hugo Chavez, Maduro's mentor who ruled from 1999-2013.

A local monitoring group, the Venezuelan Conflict Observatory, said it had registered 187 protests in 20 states by 6 p.m. on Monday with "numerous acts of repression and violence" carried out by paramilitary groups and security forces.