JOHANNESBURG — Police fired tear gas at a crowd of Kenyan ferry commuters as the country’s first day of a coronavirus curfew slid into chaos. Elsewhere, officers were captured in mobile phone footage whacking people with batons.

Virus prevention measures have taken a violent turn in parts of Africa as countries impose lockdowns and curfews or seal off major cities. Health experts say the virus’ spread, though still at an early stage on the continent, resembles that of Europe, adding to widespread anxiety. Cases across Africa were set to jump above 4,000 on Saturday.

Abuses of the new measures by authorities are an immediate concern.

Minutes after South Africa’s three-week lockdown began on Friday, police screamed at homeless people in downtown Johannesburg and went after some with batons. Some motorists were pursued, stopped, searched and called “selfish.” Other citizens reported the police use of rubber bullets. Fifty-five people across the country were arrested.

In Rwanda, the first country in sub-Saharan Africa to impose a lockdown, police have denied that two civilians shot dead Monday were killed for defying the new measures, saying the men attacked an officer after being stopped.

And now Zimbabwe, where police are widely criticized by human rights groups for deadly crackdowns, enters a three-week lockdown on Monday as the country’s handful of virus cases already threatens to overwhelm one of the world’s most fragile health systems.