At least 50 members of the Economic Freedom Fighters were rushed to hospital after police allegedly opened fire on them during a march in Johannesburg on Tuesday, the party's regional chairman said.
"An army of heavily armed SAPS police opened fire without warning at a group of peaceful EEF protesters outside Jubert Park injuring 50 people who had to be rushed to Hillbrow clinic," Musa Novela said in a statement.
He described the act as "barbaric".
He said EFF members were marching peacefully in Johannesburg ahead of the vote of no confidence in President Jacob Zuma when the incident happened.
"This ruthless and inhuman act.... [happened] when the EFF launched a day of action... calling on all the cowardly ANC MPs' to apply their conscience and vote against the corrupt and unethical president."
Marches were held throughout the country on Tuesday in the build-up to the vote of no-confidence.
News24 reported that groups for and against Zuma had gathered in different provinces.
In the Cape Town CBD, ANC, EFF and DA supporters – as well as some from several other political parties, and residents interested in the vote – gathered on the Grand Parade before making their way to Parliament.
Cape Town Mayor Patricia de Lille was among the hundreds who marched to Parliament.
Security was tight in the city centre, with police officers monitoring the crowds.
Gatherings were also reported in other parts of the country including in Johannesburg, Durban and Port Elizabeth.
Viewing areas for the vote have been set up in some parts.