0511 GMT April 21, 2018
The clashes erupted as police in the beleaguered oil-rich nation tried to disperse thousands of marchers as they reached a vital Caracas freeway, edging back slightly as masked protesters pelted them with stones and Molotov cocktails, AFP reported on Friday.
Demonstrators vowed not to flinch in their campaign to oust Maduro, despite three weeks of violent protest that has seen eight people killed, three of them on Wednesday.
Protesters set fire to trash bins and tore down a billboard to use as a barricade as officers fired water cannon at them and a police helicopter hovered overhead.
Clashes also broke out in the flashpoint western city of San Cristobal, Maracaibo in the northwest and Valencia in central Venezuela.
Late Thursday the government and opposition traded blows over events at a maternity hospital that prompted the evacuation of some 50 children.
The government said it was due to an attack by armed gangs, but the opposition blamed it on tear gas used to quell unrest.
The opposition called for new protests, a "march of silence" in all parts of the country on Saturday and a national road blockage on Monday.
Protesters blame Maduro – heir of the leftist "Bolivarian revolution" launched by the late Hugo Chavez in 1999 – for an economic crisis marked by severe shortages of food, medicine and basic goods.
Maduro says the protests seeking to oust him are supported by Washington.
On Thursday, Maduro said the opposition was ready to begin dialogue, but his opponents denied the claim, saying the only way forward would be to call new elections.
In a posting on Twitter, senior opposition leader Henrique Capriles slammed Maduro as a "dictator".
"No one believes him, however, about dialogue, which the Venezuelans will do with their VOTE!" he wrote.
Pressure on Maduro has been mounting since 2014, as falling prices for Venezuela's crucial oil exports have sent the once-booming economy into a tailspin.
The crisis escalated after March 30 when the Supreme Court moved to seize the powers of the legislature, the only lever of state authority not controlled by Maduro and his allies.
The escalation of Venezuela's political crisis has galvanized the often divided opposition in its efforts to force Maduro from power.
The president, in turn, has urged his supporters, the military and civilian militias to defend the "revolution."
International concern over the situation is growing, with UN Secretary General Antonio Guterres on Thursday urging all sides to make "concrete gestures" to ease the tension and the European Union urging the parties to "de-escalate" the conflict.
The opposition has urged the military – a pillar of Maduro's power – to abandon him.
But Defense Minister General Vladimir Padrino Lopez has pledged the army's "unconditional loyalty."