Police in Zimbabwe fired tear gas and water cannon to disperse scores of opposition supporters demanding fair elections next year.

Around 100 young supporters of the Movement for Democratic Change (MDC) took to the streets of Harare on Wednesday to protest against what they say are plans by the country's electoral body to ensure a victory for 93-year-old President Robert Mugabe.

Riot police attempted to stop protesters from marching in the city centre, firing tear gas canisters and water at activists and shoppers from police trucks.

Some young people set fire to cardboard on the streets but police quickly doused the flames with water.

"Heavily armed police officers brutally crushed our peaceful demonstration," MDC youth secretary general Lovemore Chinoputsa said in a statement.

Al Jazeera's Haru Mutasa, reporting from Harare, said: "There is a nationwide ban on protesting. People are not allowed to come out to the streets and show that they are angry."

A truck spraying water cannon fired towards our correspondent as she was reporting.

"Riot police and water cannon trucks are driving around the city trying to disperse people. People are running for cover," Mutasa said.

Police spokesman Paul Nyathi said "some people" who had been "causing disturbances" were arrested.

The MDC wants the electoral commission to create a new voters' roll and increase the number of locations where voters can register in urban strongholds.

Morgan Tsvangiri, the opposition leader, says he is worried Mugabe's Zanu-PF party wants to rig the elections.

'Zimbabweans denied voting rights for 37 years'

"People went out there to fight for one person, one vote to empower Zimbabweans," he said. "Over the last 37 years [Zanu PF has] denied Zimbabweans the right to vote. They have put all efforts at preventing Zimbabweans from voting."

According to the constitution adopted in 2013, Mugabe is allowed to run for a final five-year term next year. He has been in power since independence in 1980.

Mugabe denies allegations of vote rigging.

Tsvangiri's plans to stage a fourth attempt to try and remove Mugabe from power next year, but some analysts say his party needs a new strategy.

"The MDC has not been able to fully utilise the capital they have, popular support and the critical numbers of masses following them," Earnest Mudzengi, director of the Media Centre, a training organisation for journalists, told Al Jazeera.

Mugabe is currently in Singapore for medical treatment.