The City of Joburg on Thursday night announced a breach of its network on and shut down its website and all e-services as a precautionary measure.
In a tweet, the City said it had detected a network breach "which resulted which resulted in an unauthorised access to our information systems".
Business Day reported that the attack comes hours after the City received a bitcoin ransom note from a group called the Shadow Kill Hackers.
The hack reportedly occurred at the same time that several banks also reported internet problems believed to be related to cyber attacks.
The City further tweeted: "The incident is currently being investigated by City of Joburg cyber security experts, who have taken immediate and appropriate action to reinforce security measures to mitigate any potential impacts. As a result several customer facing systems - including the city's website, e-services, billing system - have been shut down as a precaution.
"As a result, several customer-facing systems - including the City's website, e-services; billing system... has been shut down as a precautionary measure."
The City said the shutdown would last for 24 hours and meant that customers would not be able to transact on e-services or log queries at the call centre.
According to Business Day, the note on Twitter came after several city employees received the ransom note, which reads: "All your servers and data have been hacked. We have dozens of back doors inside your city.
We have control of everything in your city. We also compromised all passwords and sensitive data such as finance and personal population information."
The hackers reportedly demand the payment of 4.0 bitcoins by October 28 at 17:00 failing which they will upload all the data on to the internet.
Some of South Africa's banks also reported having online issues on Thursday.
Standard Bank tweeted: "You may be finding it difficult to log on to Internet banking and our Banking App at the moment. We're working to sort this out."
ABSA similarly tweeted: We are aware of the ongoing intermittent issues with our digital channels and our technicians are working on a fix. We will let you know as soon as that is resolved and we're up and running again. Apologies for any inconvenience caused."
Both banks have since reported that the issues had been resolved.