Venezuela's Supreme Court has ruled that it will take over the opposition-led Congress' legislative powers, in a move condemned by opposition parties as an attempt to install a dictatorship.

The court, which has consistently sided with President Nicolas Maduro's administration, said late on Wednesday that as long as the Congress remains in "contempt" of past court rulings "congressional functions will be exercised by this chamber or another chosen organ".

The dispute centres on three legislators banned over vote fraud accusations.

Maduro critics say it is an excuse for the government to muzzle opposition during a mounting economic crisis in the oil-rich country.

The Democratic Unity organisation, an opposition bloc, criticised the Supreme Court's decision on Thursday, with several legislators accusing Maduro of acting like a dictator.

"This unconstitutional sentence that we reject ... cements another step in the dismantling of Venezuela's democracy," the opposition said in a statement.

"This government is dying, and that's why it's turning to these desperate measures."

"Nicolas Maduro has staged a coup in Venezuela," Congress Speaker Julio Borges said in a fiery speech outside the National Assembly. "This is a dictatorship."

International condemnation

The head of the Organisation of American States (OAS), a bloc of 34 independent countries including Venezuela, also accused Maduro's government of carrying out a "self-coup".

"The sentences from the Supreme Court ... are the final blows with which the regime subverts the constitutional order of the country and finishes with democracy," said OAS Secretary-General Luis Almagro in a statement.

The United States described the move as a "serious setback for democracy in Venezuela" while the European Union called for a "clear electoral calendar" going forward.

The opposition promised new street protests starting from Saturday.

Around a dozen opposition lawmakers trying to march to the Supreme Court on Thursday clashed with National Guard soldiers and pro-government supporters lined up to stop them.

Pockets of youths took to the streets in parts of Caracas and attempted to block a major highway. However, numbers were small and they quickly dispersed.

Maduro, a 54-year-old former bus driver and foreign minister, was narrowly elected in 2013 to replace late leftist president Hugo Chavez.

Under his rule, the country has slipped into severe recession, with soaring inflation and acute shortages of food and medicine.