The motives for the shootings near Johannesburg and Cape Town were unknown, but gang violence and organised crime remain rife in South Africa, despite government efforts to curb one of the highest per-capita murder rates in the world.
In Wedela township, about 80km from Johannesburg, 17 people were killed and 15 injured at a tavern when suspects armed with AK-47 rifles opened fire about 9.30pm (1930 GMT) on Saturday, according to police.
Many residents were reluctant to speak about the incident, but one said illegal miners, known locally as zama zamas from an isiZulu expression for "taking a chance", live in the area, where gold is mined and which experts say is a hotspot for gun crime.
Soldiers from the national army and police pathologists had arrived in the township, where two burnt vehicles could be seen.
The tavern where the shooting happened had a sign that read "No weapons allowed" below its trading hours.
At the scene of the shooting in Lwandle, on the outskirts of Cape Town, onlookers had gathered behind police lines but did not want to speak to journalists, saying they feared for their safety.
In that incident, gunmen opened fire in a venue selling grilled meat about 2am on Sunday, killing 10 people and injuring 11 more.
No arrests have been made yet and detectives are working to find the gunmen, police said in statements.
"South Africa has a serious illegal firearms problem, and firearms are frequently used by organised criminal groups as well as in gang-related and other violent crimes," crime expert Yusuf Abramjee said.
"Every mass shooting should therefore trigger more than an investigation into the immediate perpetrators," he told Reuters.
"Authorities need to look at the wider networks behind the violence."
Crime is expected to be a major issue for voters in municipal elections in November, when the African National Congress is facing further erosion of voter support.
President Cyril Ramaphosa said earlier this year organised crime had become the biggest threat to South Africa's democracy, and deployed the army to help police in some areas.
A shooting at a house party near Durban last week killed 11 people, while a series of women's bodies found near Johannesburg since July has renewed fear and anger over high rates of femicide.
