The patchy service was a result of faults in the under-sea cables that connect the region to the rest of the world through South Africa, industry expert Ben Roberts told the BBC.
A similar outage was experienced in parts of West and Southern Africa in March.
On Monday, some East Africans were still experiencing slow internet speeds with some telecom providers indicating that the issue was yet to be fully resolved and asking subscribers to be patient.
“We are still working with the undersea fibre cable team to have them resolve the issue,” Airtel Kenya responded to a Kenyan user concerned about the problem.
Vodacom Tanzania sent a similar message on social media to such queries.
Cloudflare Radar, which monitors internet connectivity, on Sunday said that Tanzania was one of the worst-affected countries with traffic falling to 30% of expected levels.
Tanzania’s Citizen newspaper described what has happened as an “internet blackout [that] has affected major network channels”.
On X, formerly known as Twitter, service providers have been fielding queries from frustrated customers.
In response to one Kenyan user who wanted to know if they would be able to watch Sunday’s Manchester United versus Arsenal English Premier League match, Airtel Kenya said its team was working on the “network issue” and apologised.
Safaricom, also in Kenya, said it was “experiencing a challenge”.
Airtel Ugandan has said it was aware of the “intermittent internet service”. And MTN Rwanda said there was “an issue of degradation of international links”.
Malawi, Mozambique and Madagascar have also been affected according to Cloudflare Radar.
Mr Roberts, from the pan-Africa company Liquid Intelligent Technologies, said that he had confirmed that one cable that runs alongside the coast of East Africa, known as Eassy, had been cut earlier on Sunday some 45km (28 miles) north of the South African port city of Durban.
Another cable was also cut. He ruled out the idea that it could be sabotage and said it was rather an unhappy coincidence.
Other cables linking East Africa to Europe are also available and gradually the service should improve as data is re-routed.
But as a lot of big companies have data centres in South Africa the damage to the vital link that Eassy provides had a big impact.
In March, widespread outages were reported in countries including South Africa, Nigeria, Ivory Coast, Liberia, Benin, Ghana and Burkina Faso.
This was also put down to cable failures.
The cause was not clear but led to the frustration of millions of customers around the continent.
Source: https://www.graphic.com.gh/tech-news/internet-outage-felt-across-east-africa.html