It is not the first instance of a South African bank apparently failing to manage the huge migration of customers to online banking. In March First National Bank had to weather a storm of protest when it suffered a systems failure for several hours.

On Friday an Absa spokesman said the bank's system engineers were trying to resolve the problem, but by 3.45pm the website was still not accessible after being unavailable all morning.

"We are experiencing technical difficulties. We are awaiting feedback. We are aware it is month-end and that a lot of people want to transact," she said.

Transaction systems in Absa branches were not affected.

An electricity spike that affected FNB's main production and backup system was blamed for its downtime in March. But City Power, the Johannesburg electricity utility, denied it had caused the failure.

Absa said late on Friday that access across its mobile and internet banking channels had been only partially restored but just before 6pm it said that the problem had been rectified and the service restored across Absa's online and mobile banking channels.

"Absa experienced a technical issue on Friday morning which had the potential to slow or stop customers accessing internet and mobile banking platforms," the spokesman said.

But the bank cautioned that as the system regained stability users might experience slower than normal response times when loading certain pages.

To assist customers, Absa Internet Banking extended the cut-off time for payments till 6pm on Friday.

Absa branches were roped in to assist customers who had been affected by the downtime.

Customers were also urged to use Absa branches or its ATM network during this period.