Police fired tear gas and beat protesters who responded by throwing stones in Zimbabwe's capital Harare on Friday in the latest of a string of highly charged demonstrations.
The violence came as a High Court judge ordered police "not to interfere (with), obstruct or stop the march".
Dozens of police blocked off the site of an opposition rally for electoral reforms by 2018, when 92-year-old President Robert Mugabe who has ruled the southern African country for decades will seek re-election.
Mugabe's opponents have become emboldened by rising public anger and protests over an economic meltdown, cash shortages and high unemployment.
Zimbabwean police fired tear gas and water cannons at opposition leaders and hundreds of demonstrators before unrest swept across large parts of the capital Harare.
Demonstrators began throwing stones at police while some set tyres ablaze and others pulled down the sign for a street named after Mugabe.
Some people caught up in the melee, including children going to a nearby agricultural show, ran for shelter in the magistrate's court while riot police pursued the protesters and threatened journalists covering the rally.
The usually-bustling pavements were clear of street hawkers and some shops were shut, as rocks, sticks and burning tyres were strewn across the streets.
Opposition protesters also clashed with supporters of the ruling ZANU-PF party who had refused to clear their street stalls.
ZANU-PF youths hurled stones at the opposition activists but were overpowered and their stalls set on fire.
Mugabe slammed the protests and accused foreign powers of having a hand in the unrest.
"They are burning types in the streets in order to get into power. They are thinking that what happened in the Arab Spring is going to happen in this country, but we tell them that is not going to happen here," said Mugabe in remarks broadcast by state television.
'Very deep anger'
The march was organised by 18 opposition parties including the Movement for Democratic Change led by Morgan Tsvangirai and the Zimbabwe People First formed this year by former vice president Joice Mujuru.
Opposition leaders condemned the brutal repression of the protest and vowed to increase pressure on Mugabe's regime.
"If that was meant to cow us from demonstrating, I want to say we are going to do the same next week Friday," former Mugabe ally and ex-cabinet minister Didymus Mutasa told reporters.
Protests "will continue until the day we vote," said Mutasa, a former top member of ZANU-PF who is now a senior member of Mujuru's party.
"We have had enough of ZANU-PF misrule."
Tsvangirai said the public would not be easily calmed.
"The people's anger is very deep. The people's desperation is very deep," he said.
"Today's brutal suppression of the people will not stop them from exercising their rights."
Friday's march was to demand free and fair elections. The last elections in 2013 were won by Mugabe in a vote the opposition said was rigged.
Zimbabwe has seen a mounting tide of violent protests in recent weeks, with demonstrators demanding the resignation of Mugabe, who has been in power since 1980.
Under his rule, there has been an economic collapse that has caused food and cash shortages, with the country battling to pay public servants.