MMUSI Maimane, national spokesman for the Democratic Alliance (DA), laid charges against the Congress of South African Trade Unions (Cosatu) on Wednesday after a protest by the party turned violent in Johannesburg.

Charges of incitement of violence, intimidation and illegal gathering were laid at the Hillbrow police station at noon.

The DA would analyse footage of the march to try to identify individual perpetrators, DA spokeswoman Kelly Miller said.

"We hope, first of all, that we must all accept the rule of law, and we must accept that everything we do must be within legal parameters," Mr Maimane said.

Rocks and pieces of cement flew in a confrontation between DA and Cosatu supporters in Braamfontein on Tuesday. Police used tear gas and water cannons to disperse Cosatu members who stopped the DA from protesting outside its headquarters.

Ms Miller said four party members were hospitalised and a number of others injured.

The DA wants Cosatu to stop stonewalling a government youth wage subsidy that, it argues, would create thousands of jobs for young people.

Mr Maimane said Cosatu had behaved "undemocratically".

"They (Cosatu) came out in their numbers, holding an illegal march, and holding in contempt the idea that the youth wage subsidy should be considered," he said, adding that the trade-union federation was not contesting the subsidy because it had not presented an alternative.

"They have made it a contest of people, a contest of class," he said. "For the benefit of our democracy, we must make it a contest of ideas."

A working environment must be created to address the concerns of South Africa's young people. "The issue we are going to fight for is that people must be employed," Mr Maimane said.

The march, led by DA officials including party leader Helen Zille, youth leader Makashule Gana, parliamentary leader Lindiwe Mazibuko and Mr Maimane, began peacefully. But in Jorissen Street, Braamfontein, protesters were met by Cosatu members moving down the street from Cosatu's offices opposite the Joburg Theatre.

For an hour, the two groups traded insults, with a cordon of police keeping them apart.

When rocks and pieces of cement were thrown into the crowd during Ms Zille's speech and a DA member on the VIP truck was seriously injured, the DA retreated to Jan Smuts Avenue.

Cosatu members then chased DA supporters and police had their hands full trying to control groups intent on hounding blue-shirted protesters out of the area.

Police eventually sprayed tear gas and fired a water gun to break up the Cosatu crowd.