It is not clear what has caused the new disruption.
Large parts of West Africa are struggling to get back online following damage to an undersea cable.
The fault has caused severe problems in Benin, Togo, Niger and Nigeria.
The blackout is thought to have been caused by damage to the SAT-3 cable which runs from Portugal and Spain to South Africa, via West Africa.
Around 70% of Nigeria's bandwidth was cut, causing severe problems for its banking sector, government and mobile phone networks.
"SAT-3 is currently the only fibre optic cable serving West Africa," explained Ladi Okuneye, chief marketing officer of Suburban Telecom, which provides the majority of Nigeria's bandwidth.
"So all West African countries have to use it."
Companies were being forced to use alternatives - such as using satellite links - to maintain connections to the rest of the world, he said.
Telkom South Africa, one of the shareholders of SAT-3, has not said what caused the problems but said it was aware of "a cable fault on the Benin branch that is being investigated".
The 15,000km (9,300mile) SAT-3 cable lands in eight West African countries as it winds its way between Europe and South Africa.
"The rest of the system is unaffected by this fault," a Telkom South Africa representative said.
Nigeria has been badly hit because around 70% of its bandwidth is routed through neighbouring Benin.
The network, run by Suburban Telecom, was set up to bypass Nigeria's principal telecoms operator Nitel which runs the SAT-3 branch cable which lands in Nigeria.
The SAT-3 consortium is in the process of sending a ship from Cape Town in South Africa to the area to investigate the fault.
Mr Okuneye said that by the time the relevant paperwork was done, it was likely to be "two weeks" before the ship arrived off the coast.
Meanwhile, Benin has been able to reroute its net traffic through neighbouring countries to get back online.
Mr Okuneye said his company was hoping to do the same but said the process would be slower because its bandwidth requirements were so much larger than those of the small republic.
Togo and Niger, which are not part of the SAT-3 consortium, remain offline.