Caracas: Protesters have blocked streets in Caracas with broken concrete, twisted metal and flaming piles of rubbish in opposition to the Venezuelan president's bid to rewrite the constitution.

Amid a rapidly escalating political crisis, socialist President Nicolas Maduro signed a decree on Monday to begin the process of rewriting the charter.

Opposition leaders called the planned constitutional assembly a ploy to put off regional elections scheduled for this year and a presidential election that was to be held in 2018.

Polling suggests the socialists would lose both elections badly amid widespread anger over triple-digit inflation and shortages of food and other goods.

The opposition-majority congress on Tuesday officially rejected Maduro's move to call a constitutional congress, saying the idea should first be put to a vote of Venezuelans.

Congress president Julio Borges called a constitutional assembly a "giant fraud" by Maduro and his allies designed to keep them in power.

Maduro hinted some members of the assembly would be selected by voters but many observers expect the selection process to favour the socialists.

"This will be a citizens' assembly made up of workers," he said.

In Washington, senior US state department official Michael Fitzpatrick said the bid for a constitutional assembly "overrides the will of the Venezuelan people and further erodes democracy".

Meanwhile, police repressed scattered protests on Tuesday with tear gas, as they have nearly daily for weeks.

Residents manning barricades choking streets across the capital vowed to protest until Maduro leaves office.

At least 29 people have died in unrest during the past month and hundreds have been injured.

The opposition has called for another major demonstration on Wednesday.

The wave of unrest began in reaction to an attempt to nullify the opposition controlled-congress but has become a vehicle for people to vent their fury at Venezuela's economic ruin and violent crime.

Venezuela's constitution was last rewritten in 1999, early in the 14-year presidency of the late Hugo Chavez, who launched a socialist revolution in the oil-exporting nation.

AP