Zimbabwean police used tear gas, water cannons and fired in the air to disperse an opposition rally protesting police brutality in the capital Harare on Wednesday.
Many protesters were reported to have been injured, but police spokeswoman Charity Charamba said she had no information on that.
Protesters looted a supermarket belonging to the vice president and stoned a vehicle emblazoned with the portrait of President Robert Mugabe, witnesses said.
Demonstrators also set two vehicles on fire and stoned police during what Charamba described as an unauthorized rally.
"We want to warn Mugabe that we want you to leave office immediately," said Happymore Chidziva from the main opposition party Movement for Democratic Change.
"We are going to stage protests until you leave office, and we are not going to seek any police clearance," Chidziwa told dpa.
The rally took place two days before a planned march by all opposition parties to pressure Mugabe to implement electoral reforms ahead of the 2018 vote.
Thee southern African country has seen months of protests against alleged human rights abuses and the deterioration of the economy under the 92-year-old president, who has ruled Zimbabwe since 1980.