Venezuelan police have fired tear gas against anti-government protesters in Caracas demanding a referendum to recall embattled President Nicolas Maduro.
Thousands have marched in several cities in what is expected to be the biggest wave of opposition rallies.
Mr Maduro has rejected a referendum drive amid growing discontent with the country's spiralling economic crisis.
He has announced a 60-day state of emergency, giving soldiers and police wider powers.
In the third day of demonstrations in a week, opposition leader Henrique Capriles called for a march onto the headquarters of the National Electoral Council (CNE), in Caracas.
But security forces were out in force, and used tear gas to control a group of protesters who tried to break a police line.
"With these extreme measures, the government reveals its weakness," said the speaker of the opposition-held National Assembly, Henry Ramos Allup.
In the morning rush hour, 14 underground stations were closed in the capital.
Officials said the closures were due to technical issues but opponents said it was a government effort to prevent people from joining their demonstrations.
Hundreds of Maduro supporters were also seen in Caracas but there were not reports of clashes between the opposing groups.
Venezuela is facing a serious economic crisis, with high inflation and shortage of many basic goods.
Mr Maduro has accused the country's elite of boycotting the economy to achieve its political goals.
But the opposition blames the mistaken policies of Mr Maduro and his predecessor, Hugo Chavez, for the crisis.
Mr Maduro was elected in 2013 for a six-year term, following the death of Mr Chavez.
On 2 May, the electoral body received a petition signed by 1.85 million people demanding a referendum to oust Mr Maduro.
The constitution says a referendum will be called to decide if the president remains in power if a second petition is signed by at least 20 percent of the electorate, or nearly four million people.
But the government has already made it clear that the referendum will not go ahead.
On Tuesday, Mr Maduro told journalists the opposition demonstrators would not be allowed to march through the streets of the Libertador neighbourhood, where the CNE building is located.
"They will not impose a referendum using violence to blackmail us," Mr Maduro said.
The move angered the opposition, which says it was seeking a legal and constitutional manner to achieve political change.
On Friday (local time), Mr Maduro issued a decree declaring a state of emergency for 60 days, renewable for an equal period of time.
He said he needed the extra powers conceded by the decree to deal with the political and economic crisis.