Sporadic clashes occurred on Thursday as tens of thousands of demonstrators shut down much of Venezuela's capital for a third day in protest of what they call an attempted coup by socialist President Nicolas Maduro.

Many carried signs reading "No to Dictatorship" as they braved the choking tropical heat on the principal highway that cuts from Caracas' wealthy eastern section to downtown.

Protesters hurled stones at riot police who fired tear gas and water cannon, prompting chaos on the eight-lane highway.

There were no immediate reports of injuries.

READ MORE: Anti-Maduro protesters clash with police in Caracas

Venezuela has seen near-daily protests since the Supreme Court issued a ruling nullifying Congress last week, a move the opposition has called an internal "coup d'etat".

While the widely condemned decision was quickly overturned, the opposition has stepped up street protests against Maduro. In a major confrontation on Tuesday, some 20 people were injured and 18 arrested during clashes.

Thursday's demonstration, dubbed a "traffic jam against the coup", was an attempt to show the government that the opposition will not let up pressure until early national elections are called.

"When I left this morning, my grandkids said: 'Grandma, aren't you scared?' But I told them you cannot let yourself be intimidated. You have to get rid of this government," said Asusena Aquilera, 57, a retired finance worker who added she struggles to get enough to eat amid food shortages.

The South American country is suffering from triple-digit inflation, shortages of basic foods and medicines, and one of the world's highest murder rates.

Maduro's government has said a US-backed business elite is responsible for Venezuela's economic downturn, and it is trying to foment a coup to impose right-wing rule.

His supporters also rallied in Caracas on Thursday by creating a traffic jam of its own and closing more than a dozen metro stations.

Socialist Party official Freddy Bernal denounced opposition leader Henrique Capriles.

"Mr Capriles, you're trying to ignite the country," Bernal said. "You're looking for deaths. Don't then come like a sissy saying that you're a political prisoner. Don't then come crying that you're being persecuted."

Not since 2014's major unrest has the opposition held such sustained demonstrations, despite protester fatigue, fear of violence, and the necessity for so many Venezuelans to spend much of their day looking for food.

READ MORE: Police crack down on protests after 'power grab'

Although Maduro has retained the crucial support of the army so far, that could be changing, political analyst Luis Salamanca said.

"At this point, Maduro can't say he's sure of anyone's support, including the armed forces," he told AFP news agency.

Caracas saw two similarly large anti-government demonstrations last fall, but protesters on Thursday said they thought this time might be different, with steady protests combined with escalating international criticism and rapidly worsening shortages.

"This time we are not going to let up the pressure. I can't believe the government has been sitting with its arms crossed watching this country just fall apart," said maintenance worker Freddy Munoz as he ate a tamarind slush to cool down.

"I have three little kids at home. We can't find them milk."